Fluorescence image display apparatus

ABSTRACT

A fluorescence image display apparatus is provided; wherein, when a pseudo color image representing the tissue state of a target subject is obtained, based on a fluorescence image emitted from the target subject upon the irradiation thereof by an excitation light, the tissue state can be recognized regardless of the intensity of the fluorescent light. Based upon the statistical quantity of a wide band fluorescence image computed by a statistical quantity computing means, a gain that the wide band and narrow band fluorescence image data are to be multiplied by is computed by a gain computing means. A gain multiplying means multiplies the wide band and narrow band fluorescence image data by the gain, whereby a green gradation is assigned to the wide band fluorescence image and a red gradation is assigned to the narrow band fluorescence image, and a composite image data is obtained by an image composing means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a fluorescence image displayapparatus, and in particular to a fluorescence image display apparatusfor measuring the fluorescent light emitted from a target subject uponthe irradiation thereof by an excitation light and displaying as animage the data relating to said target subject.

2. Description of the Related Art

Fluorescent light detection apparatuses have been proposed that make useof the fact that the intensity of the fluorescent light emitted from anormal tissue differs from the intensity of the fluorescent lightemitted from a diseased tissue when a target subject (i.e., a livingtissue) is irradiated by an excitation light within an excitationwavelength range of the intrinsic fluorophores of the target subject,wherein, by detecting the fluorescent light emitted from a targetsubject upon irradiation thereof by an excitation light within apredetermined wavelength range, the location and range of penetration ofa diseased tissue is discerned.

Normally, when a target subject is irradiated by an excitation light,because a high-intensity fluorescent light is emitted from a normaltissue, as shown by the solid line in FIG. 26, and a weak-intensityfluorescent light is emitted from a diseased tissue, as shown by thebroken line in FIG. 26, by measuring the intensity of the fluorescentlight emitted from the target subject, it can be determined whether thetarget subject is in a normal or a diseased state. These types offluorescence image display apparatuses are in many cases provided builtin to the configuration of an endoscope for insertion into a body cavityof a patient, a colposcope, or a surgical microscope.

However, for cases in which the intensity of the fluorescent lightemitted from a target subject upon the irradiation thereof by theexcitation light is to be displayed as an image, because there isunevenness on the surface of a target subject, the intensity of theexcitation light irradiating the target subject is not of a uniformintensity. Further, although the intensity of the fluorescent-lightemitted from the target subject is substantially proportional to theintensity of the excitation light, the intensity of the aforementionedexcitation light becomes weaker in inverse proportion to the square ofthe distance between the excitation light and the target subject.Therefore, there are cases in which the fluorescent-light received froma diseased tissue located at a position closer to the excitation lightsource than a normal tissue is of a higher intensity than thefluorescent-light received from aforementioned normal tissue, and thestate of the tissue of the target subject cannot be accurately discernedbased solely on the data relating to the intensity of thefluorescent-light received from the target subject upon the irradiationthereof with an excitation light.

In order to remedy the problems described above, methods such as thatdescribed in the specification of U.S. Pat. No. 5,647,368, wherein bycolorizing and synthesizing a fluorescence image obtained by irradiatinga target subject with an excitation light having a wavelength in thewavelength range near 500 nm, upon which the intensity of thefluorescent light emitted from the target subject changes by a largedegree depending on the tissue state of the target subject, with afluorescence image obtained by irradiating the target subject with anexcitation light having a frequency in the wavelength range near 630 nm,upon which the intensity of the fluorescent light emitted from thetarget subject exhibits no change depending on the tissue state of thetarget subject, to obtain a colorized synthesized image; when saidcolorized synthesized image is displayed, the tissue state of the targetsubject can be accurately discerned based on the visually recognizablecolor thereof, have been proposed.

Further, there has been proposed, as described in Japanese UnexaminedPatent Publication No. 2001-157658, a method of colorizing anddisplaying two types of fluorescence images based on the irradiation ofa target subject with two different wavelengths of excitation light (anarrow band excitation light having a wavelength near 480 nm, and a wideband excitation light having a wavelength within the wide band of430–730 nm). According to this method, because the band of thefluorescent light is wider in comparison to the method proposed in theaforementioned U.S. Pat. No. 5,647,368, the S/N ratio of the imagesobtained by additive color mixture can be improved, and because theintensity of the fluorescence images changes by a large amount inaccordance with the tissue state of the target subject for both bands,the color change corresponding to the change in the tissue state can bemade more distinct, whereby the distinguish ability of the tissue stateis improved a level.

However, according to the above described methods of displayingcolorized synthesized images, the color of the image to be displayed isregulated by a chromaticity, which is determined in correspondence tothe of the ratio of the two types of fluorescence images that are to becolor added and mixed, and a luminosity, which is determined incorrespondence to the intensity of the fluorescence images. Because thechromaticity of the image to be displayed is determined incorrespondence to the ratio of the two types of fluorescence images thatare to be color added and mixed, the chromaticity of the image that isto be displayed, which corresponds to the tissue state of the targetsubject, can be determined at once. However, because the fluorescentlight intensity differs according to the distance between the lightsource and the target subject, the luminosity of the image to becolorized differs according to the aforementioned distance. Here, thesetypes of fluorescence image display apparatuses are in many casesprovided in the configuration of an endoscope for insertion into a bodycavity of a patient, a colposcope, or a surgical microscope; because theobjective of the use thereof is the measurement of an internal portionof a body cavity, the distance between the target subject and any ofsaid apparatuses is between several to 50 mm. Therefore, if the distancebetween the distal end of the insertion portion that is inserted intothe body cavity of a patient and the target subject changes, theintensity of the fluorescent light changes; as a result, the luminosityof the synthesized image changes. If the luminosity of the colorizedsynthesized image changes in this manner, because the color appearing inthe displayed color added and mixed image will be recognized as adifferent color even if the chromaticity thereof is the same, there is afear that even though tissues have the same tissue state, said tissueswill be discerned to have different tissue states. On the other hand,for cases in which the luminosity of the image to be colorized is low,there are cases in which even though a chromaticity is different, thecolor in the displayed colorized synthesized image cannot be recognizedto be different, giving rise to a fear that a diseased portion might beoverlooked.

SUMMARY OF THE INVENTION

The present invention has been developed in consideration of theforgoing circumstances, and it is an object of the present invention toprovide a fluorescence image display apparatus capable of displaying afluorescence image wherein it is possible to accurately discern,regardless of the intensity of the fluorescent light, the tissue stateof the target subject depicted therein.

The first fluorescence image display apparatus according to the presentinvention comprises a fluorescence image obtaining means for irradiatinga target subject with an excitation light and obtaining two fluorescenceimage data, each formed of fluorescent light of a mutually differentwavelength band, based on the fluorescent light intensity emitted fromthe target subject upon the irradiation thereof by the excitation light,

a gain computing means for computing, based on the statistical quantityof either one of said two fluorescence image data, a gain that said twofluorescence image data are to be multiplied by,

a multiplying means for multiplying said two fluorescence image data bysaid gain and obtaining two multiplied fluorescence image data, an imageforming means for forming, based on said two multiplied fluorescenceimage data, a pseudo color image data representing a pseudo color imagereflecting the tissue state of the target subject, and an image displaymeans for displaying said pseudo color image.

Here, the expression “based on the statistical quantity of either one ofsaid two fluorescence image data, a gain that said two fluorescenceimage data are to be multiplied by” refers to, for example: in a case inwhich the statistical quantity of the fluorescence image data is smallerthan a desired value, that is, when the size of the data value of thefluorescence image data is not large enough, the a gain is computed sothat the data value of the multiplied fluorescence image data becomes alarger value than that of the fluorescence image data, whereby thestatistical quantity of the multiplied fluorescence image data becomesgreater than or equal to the aforementioned desired value; for a case inwhich the statistical quantity of the fluorescence image data is largerthan a desired value, that is, when the size of the data value of thefluorescence image data is too large, a gain is computed so that thedata value of the multiplied fluorescence image data becomes a smallervalue than that of the fluorescence image data, whereby the statisticalquantity of the multiplied fluorescence image data becomes less than orequal to the aforementioned desired value; and, for a case in which thestatistical quantity of the fluorescence image data is substantiallyequivalent to a desired value, that is, when the size of the data valueof the fluorescence image data is adequately large, a gain is computedso that the data value of the multiplied fluorescence image data becomessubstantially equivalent to that of the fluorescence image data.

More specifically, the gain can be computed by use of the followingformulas (1) or (2). That is to say, if the dynamic range of the displaymeans is designated as DR (e.g., 255 in the case of data formed of eightbits), the largest value of the fluorescence image data as Max, thesmallest value of the fluorescence image data as Min, and two arbitraryconstants a (0.9–0.95), and b (e.g., 2) are designated:Gain upper limit=DR×a/{(Max+Min)/2+b×(Max−Min)/2}  (1)

Further, if the dynamic range of the display means is designated as DR,the average value of the fluorescence image data as m, the standarddeviation as σ, and two arbitrary constants a and b are designated:Gain lower limit=DR×a/(m+b×σ)  (2)

Note that if the gains that the two fluorescence image data are to bemultiplied by have a constant relationship (e.g., making the gain thatone of the two fluorescence image data is multiplied by C times thatwhich the other of the two fluorescence image data is multiplied by{where C is a constant} etc.) the gains can be of different values.

Note that according to the first fluorescence image display apparatus ofthe present invention, the image forming means can also be a means forforming the pseudo color image, based on the additive color mixturemethod, from both of the multiplied fluorescence image data.

Further, according to the first fluorescence image display apparatus ofthe present invention, the image forming means can be a meanscomprising: a color image forming means for forming a color added andmixed image data, based on the additive color mixture method, from bothof the multiplied fluorescence image data, and a color image data, basedon said color added and mixed image data, representing the chromaticcomponents of the color added and mixed image represented by said data,

a luminosity image forming means for forming a luminosity image datarepresenting a luminosity image by assigning a luminosity displaygradation to the pixel values of the multiplied fluorescence imagerepresented by either of the two multiplied fluorescence image data,

and a composite image forming means for combining the color image dataand the luminosity image data to form a composite image.

The referents of “chromatic components” include all of the following:the hue of the color added and mixed image; the color saturation, or thecolor saturation and the hue; the X,Y components of an XYZ color space;the ab components of a Lab color space; the uv components of a Luv colorspace; the a*b* components of a uniform La*b* color space; the u*v*components of a uniform Lu*v* color space; etc.

The expression “assigning a luminosity display gradation to the pixelvalues of the multiplied fluorescence image represented by either of thetwo multiplied fluorescence image data” refers to the assignment of anumerical value representing a degree of brightness to each pixel valueof the multiplied fluorescence image, corresponding to the size of eachsaid pixel value.

Further, the image forming means can be a means comprising: a colorimage forming means for forming a color added and mixed image data,based on the additive color mixture method, from both of the multipliedfluorescence image data, and a color image data, based on said coloradded and mixed image data, representing the chromatic components of thecolor added and mixed image represented by said color added and mixedimage data,

a luminosity image forming means for forming a luminosity image datarepresenting a luminosity image by assigning a luminosity displaygradation to the pixel values of the fluorescence image represented byeither of the two fluorescence image data,

and a composite image forming means for combining the color image dataand the luminosity image data to form a composite image.

Further, the first fluorescence image display apparatus according to thepresent invention can further comprise a dynamic range expanding meansfor expanding, based on the statistical quantity, the dynamic range ofboth of the multiplied fluorescence image data so that the dynamic rangethereof spans substantially the entirety of the dynamic range of thedisplay region of display means.

In this case, it is preferable that a switching means for switchingbetween a drive mode and a non-drive mode of the dynamic range expandingmeans be further provided.

Further, according to the first fluorescence image display apparatus ofthe present invention, the gain computing means can be a means forcomputing the gain based on the statistical quantity of a desired regionof the fluorescence image represented by either of the fluorescenceimage data.

Here, the referent of “a desired region” is, for example, an imageregion of an obtained fluorescence image that is an area with a highlevel of interest.

Further, according to the first fluorescence image display apparatus ofthe present invention, it is preferable that the statistical quantity beformed of at least one of the following: the maximum value of thefluorescence image data, the minimum value of the fluorescence imagedata, the average value of the fluorescence image data, a valuecombining the maximum value of the fluorescence image data and thestandard deviation, a value combining the maximum and minimum values ofthe fluorescence image data, a value combining the minimum value of thefluorescence image data and the standard deviation, and a valuecombining the average value of the fluorescence image data and thestandard deviation.

The second fluorescence image display apparatus according to the presentinvention comprises: a fluorescence image obtaining means forirradiating a target subject with an excitation light and obtaining twofluorescence image data, each formed of fluorescent light of a mutuallydifferent wavelength band, based on the fluorescent light intensityemitted from the target subject upon the irradiation thereof by theexcitation light,

a reflectance image obtaining means for irradiating a target subjectwith a reference light and obtaining a reflectance image data, based onthe intensity of the reference light reflected from the target subjectupon the irradiation thereof by the reference light,

a gain computing means for computing, based on the statistical quantityof said reflectance image data, a gain that said two fluorescence imagedata are to be multiplied by, a multiplying means for multiplying saidtwo fluorescence image data by said gain and obtaining two multipliedfluorescence image data,

an image forming means for forming, based on said two multipliedfluorescence image data, a pseudo color image data representing a pseudocolor image reflecting the tissue state of the target subject, and

an image display means for displaying said pseudo color image.

Note that according to the second fluorescence image display apparatusof the present invention, the image forming means can also be a meansfor forming the pseudo color image, based on the additive color mixturemethod, from both of the multiplied fluorescence image data.

Further, according to the second fluorescence image display apparatus ofthe present invention, the image forming means can be a meanscomprising: a color image forming means for forming a color added andmixed image data, based on the additive color mixture method, from bothof the multiplied fluorescence image data, and a color image data, basedon said color added and mixed image data, representing the chromaticcomponents of the color added and mixed image represented by said coloradded and mixed image data,

a luminosity image forming means for obtaining a multiplied reflectanceimage data by multiplying the reflectance image data by said gain, andforming a luminosity image data representing a luminosity image byassigning a luminosity display gradation to the pixel values of themultiplied reflectance image or the pixel values of the multipliedfluorescence image represented by either of the two multipliedfluorescence image data, and

a composite image forming means for combining the color image data andthe luminosity image data to form a composite image.

In this case, it is preferable that it be possible to switch the imageto which the luminosity display gradation is to be assigned between themultiplied reflectance image and either of the two multipliedfluorescence images.

It is preferable that a light that is not readily absorbable by thetarget subject, such as near-infrared light or the like be used as thereference light.

Further, the image forming means can be a means comprising: a colorimage forming means for forming a color added and mixed image data,based on the additive color mixture method, from both of the multipliedfluorescence image data, and a color image data, based on said coloradded and mixed image data, representing the chromatic components of thecolor added and mixed image represented by said color added and mixedimage data,

a luminosity image for forming means forming a luminosity image datarepresenting a luminosity image by assigning a luminosity displaygradation to the pixel values of the reflectance image or the pixelvalues of the fluorescence image represented by either of the twofluorescence image data, and

a composite image forming means for combining the color image data andthe luminosity image data to form a composite image.

In this case also, it is preferable that it be possible to switch theimage to which the luminosity display gradation is to be assignedbetween the multiplied reflectance image and either of the twomultiplied fluorescence images.

The third fluorescence image display apparatus according to the presentinvention comprises: a fluorescence image obtaining means forirradiating a target subject with an excitation light and obtaining twofluorescence image data, each formed of fluorescent light of a mutuallydifferent wavelength band, based on the fluorescent light intensityemitted from the target subject upon the irradiation thereof by theexcitation light,

a reflectance image obtaining means for irradiating a target subjectwith a reference light and obtaining a reflectance image data, based onthe intensity of the reference light reflected from the target subjectupon the irradiation thereof by the reference light,

a gain computing means for computing, based on the statistical quantityof said reflectance image data, a gain that said two fluorescence imagedata are to be multiplied by,

a multiplying means for multiplying said two fluorescence image data bysaid gain and the reflectance image data to obtain two multipliedfluorescence image data and a multiplied reflectance data,

a difference computing means for computing the difference data betweenthe multiplied reflectance image data and either of the two multipliedfluorescence image data,

an image forming means for forming, based on said difference data andthe other multiplied fluorescence image data of the aforementioned twomultiplied fluorescence image data, a pseudo color image datarepresenting a pseudo color image reflecting the tissue state of thetarget subject, and

an image display means for displaying said pseudo color image.

Note that according to the third fluorescence image display apparatus ofthe present invention, the image forming means can also be a means forforming the pseudo color image, based on the additive color mixturemethod, from both of the multiplied fluorescence image data.

Further, according to the third fluorescence image display apparatus ofthe present invention, the image forming means can be a meanscomprising: a color image forming means for forming a color added andmixed image data, based on the additive color mixture method, from thedifference data and the multiplied fluorescence image data, and a colorimage data, based on said color added and mixed image data, representingthe chromatic components of the color added and mixed image representedby said color added and mixed image data,

a luminosity image forming means for assigning a luminosity displaygradation to the pixel values of the multiplied reflectance imagerepresented by the multiplied reflectance image data or the pixel valuesof the multiplied fluorescence image represented by either of the twomultiplied fluorescence image data to form a luminosity image datarepresenting a luminosity image, and

a composite image forming means for combining the color image data andthe luminosity image data to form a composite image.

In this case, it is preferable that it be possible to switch the imageto which the luminosity display gradation is to be assigned between themultiplied reflectance image and either of the two multipliedfluorescence images.

Further, according to the third fluorescence image display apparatus ofthe present invention, the image forming means can be a meanscomprising: a color image forming means for forming a color added andmixed image data, based on the additive color mixture method, from bothof the multiplied fluorescence image data, and a color image data, basedon said color added and mixed image data, representing the chromaticcomponents of the color added and mixed image represented by said coloradded and mixed image data,

a luminosity image forming means for assigning a luminosity displaygradation to the pixel values of the reflectance image represented bythe multiplied reflectance image data or the pixel values of thefluorescence image represented by either of the two fluorescence imagedata to form a luminosity image data representing a luminosity image,and

a composite image forming means for combining the color image data andthe luminosity image data to form a composite image.

In this case also, it is preferable that it be possible to switch theimage to which the luminosity display gradation is to be assignedbetween the multiplied reflectance image and either of the twomultiplied fluorescence images.

Further, the second and third fluorescence image display apparatusesaccording to the present invention may further comprise a dynamic rangeexpanding means for expanding, based on the statistical quantity, thedynamic range of the reflectance image data and/or both of themultiplied fluorescence image data so that the dynamic range thereofspans substantially the entirety of the display means.

In this case, it is preferable that a switching means for switchingbetween a drive mode and a non-drive mode of the dynamic range expandingmeans be further provided.

Further, according to the second and third fluorescence image displayapparatuses of the present invention, the gain computing means can be ameans for computing the gain based on the statistical quantity of adesired region of the reflectance image represented by the reflectanceimage data.

Further, according to the second and third fluorescence image displayapparatuses of the present invention, it is preferable that thestatistical quantity be formed of at least one of the following: themaximum value of the fluorescence image data, the minimum value of thefluorescence image data, the average value of the fluorescence imagedata, a value combining the maximum value of the fluorescence image dataand the standard deviation, a value combining the maximum and minimumvalues of the fluorescence image data, a value combining the minimumvalue of the fluorescence image data and the standard deviation, and avalue combining the average value of the fluorescence image data and thestandard deviation.

Note that according to the first through third fluorescence imagedisplay apparatuses of the present invention: the image forming meanscan be a means for obtaining a reverse fluorescence image data byinverting the light intensity of either of the multiplied fluorescenceimage data; and forming a pseudo color image, based on this reversefluorescence image data and the other multiplied fluorescence image dataof the aforementioned two multiplied fluorescence image data.

The expression “obtaining a reverse fluorescence image data by invertingthe light intensity of either of the multiplied fluorescence image data”refers to the subtraction of the pixel value of each pixel of themultiplied fluorescence image represented by a multiplied fluorescenceimage data from the largest obtainable value of the multipliedfluorescence image data (e.g., if the data consists of 8 bits, 255), orthe computation of the reciprocal value of the pixel value of eachpixel.

Further, according to the first through third fluorescence image displayapparatuses of the present invention: the image forming means can be ameans for obtaining a reverse fluorescence image data by inverting thelight intensity of either of the multiplied fluorescence image data;multiplying the reverse fluorescence image data by a predeterminedconstant to obtain a constant-multiplied reverse fluorescence image dataand forming the pseudo color image based on this constant-multipliedreverse fluorescence image data and the other multiplied fluorescenceimage data of the aforementioned two multiplied fluorescence image data.

A value less than 1 can be used as the constant.

Note that according to the first through third fluorescence imagedisplay apparatuses of the present invention: for cases in which thefluorescence image data or the reflectance image data is represented bydata constituted of 9 bits or more, a bit shifting means can be providedfor shifting the bits of the fluorescence image data or the reflectanceimage data so that said data is expressed by the lower 8 bits thereof,and the statistical quantity computing means can be a means forcomputing the statistical quantity based on the bit-shifted data; andthe gain computing means can be a means for computing the gain based onthe statistical quantity of the bit shifted data value.

Here, the expression “shifting the bits of the fluorescence image dataor the reflectance image data so that said data is expressed by thelower 8 bits thereof” refers to the rounding off of the bit data in thecase that the fluorescence image data is expressed by 9 or more bits soas to obtain a data value of less than 8 bits; 8-bit data can becomputed by use of a common calculator.

Further, a portion or the entirety of the fluorescence image obtainingmeans of the first fluorescence image display apparatus or of thefluorescence image obtaining means and reflectance image obtaining meansof the second and third fluorescence image obtaining apparatusesaccording to the present invention can be provided in the form of anendoscope provided with an insertion portion to be inserted into a bodycavity of a patient.

Here, the expression “provided in the form of an endoscope” refers tothe disposal of a portion or the entirety of the fluorescence imageobtaining means and the reflectance image obtaining means within theinterior portion of an endoscope system. Further, the referents of “aportion” include the light emitting end for emitting the excitationlight and the reference light, and the light receiving end for receivingthe fluorescent light emitted from the target subject upon theirradiation thereof by the excitation light and the reference lightreflected from the target subject upon the irradiation thereof by thereference light.

Further, the excitation light source may be a GaN type semiconductorlaser, and the wavelength band thereof can be in the 400–420 nm range.

Note that the first through third fluorescence image display apparatusesaccording to the present invention may also be provided as apparatusescombining the additional function of obtaining and displaying a standardimage, based on the light reflected from the target subject upon theirradiation thereof by a white light.

According to the first fluorescence image display apparatus of thepresent invention: a gain that two fluorescence image data are to bemultiplied by is computed based on the statistical quantity of either oftwo fluorescence image data; two multiplied fluorescence image data areobtained by multiplying both of the fluorescence image data by thisgain; and a pseudo color image data representing a pseudo color imagereflecting the tissue state of the target subject is obtained based onboth of the multiplied fluorescence image data. Therefore, because apseudo color image can be obtained from a multiplied fluorescence imagedata having a desired data value, the pseudo color image can be formedso as to have a desired luminosity, regardless of the intensity of thefluorescent light. That is to say, the luminosity of the fluorescenceimage, which is an effect of the intensity of the fluorescent light, canbe adjusted so as to be within a desired luminosity range, whereby thedistinguishability of the tissue state of the target subject can beimproved.

According to the second fluorescence image display apparatus of thepresent invention: a gain that two fluorescence image data are to bemultiplied by is computed based on the statistical quantity of thereflectance image data representing a reflectance image formed of thelight reflected from a target subject upon the irradiation thereof by areference light; two multiplied fluorescence image data are obtained bymultiplying both of the fluorescence image data by this gain; and apseudo color image data representing a pseudo color image reflecting thetissue state of the target subject is obtained based on both of themultiplied fluorescence image data. Therefore, because a pseudo colorimage can be obtained from a multiplied fluorescence image data having adesired data value, the pseudo color image can be formed so as to have adesired luminosity, regardless of the intensity of the fluorescentlight. That is to say, the luminosity of the fluorescence image, whichis an effect of the intensity of the fluorescent light, can be adjustedso as to be within a desired range, whereby the distinguishability ofthe tissue state of the target subject can be improved. Further, becausethe intensity of said reflectance image is higher than that of thefluorescence image, the computation of the gain, which is performedbased on the statistical quantity, can be performed more adequately.

According to the third fluorescence image display apparatus of thepresent invention: a gain that two fluorescence image data are to bemultiplied by is computed based on the statistical quantity of thereflectance image data representing a reflectance image formed of thelight reflected from a target subject upon the irradiation thereof by areference light; a multiplied reflectance image data and two multipliedfluorescence image data are obtained, respectively, by multiplying thereflectance image data and both of the fluorescence image data by thisgain; the difference data between the multiplied reflectance image andeither of the two multiplied fluorescence images is computed; and apseudo color image data representing a pseudo color image reflecting thetissue state of the target subject is obtained based on the differencedata and the other multiplied fluorescence image data of theaforementioned two multiplied fluorescence image data. Therefore,because a pseudo color image can be obtained from a multipliedfluorescence image data having a predetermined data value, the pseudocolor image can be formed so as to have a desired luminosity, regardlessof the intensity of the fluorescent light. Further, by computing thedifference data between the multiplied reflectance image and themultiplied fluorescence image, the difference between the diseasedtissue and the normal tissue can be more clearly rendered. That is tosay, by adjusting the luminosity of the fluorescence image, which is aneffect of the intensity of the fluorescent light, to within a desiredluminosity range, the distinguishability of the tissue state of thetarget subject can be improved.

Further, by forming, based on the additive color mixture method, apseudo color image data from both of the multiplied fluorescence imagedata, the tissue state of the target subject can be accurately discernedbased on the visually recognized color.

Still further: by forming, based on the additive color mixture method, apseudo color image data from both of the multiplied fluorescence imagedata, and a color image data, based on said color added and mixed imagedata, representing the chromatic components of the color added and mixedimage represented by said color added and mixed image data; assigning aluminosity display gradation to the pixel values of the multipliedreflectance image or the pixel values of either of the two multipliedfluorescence images to form a luminosity image data; and combining thecolor image data and the luminosity image data to form a compositeimage; the hue of the displayed pseudo color image becomes a huereflecting the tissue state of the target subject; the luminosityreflects the light intensity for cases in which the multipliedreflectance image has been employed to form the luminosity image data,that is, the form of the target subject; and for cases in which the oneof the multiplied fluorescence image has been employed to form theluminosity image data, the luminosity reflects the tissue state of thetarget subject in addition to the form thereof. Accordingly, datarelating to the tissue state of the target subject as well as datarelating to the form of the target subject can be displayed concurrentlyin a single image. In particular, for cases in which the luminosityimage data has been formed from one of the multiplied fluorescenceimages, even for cases in which the distance between the target subjectand the light emitting end of the excitation light source iscomparatively small, if there is a diseased portion present in saidtarget subject, because the luminosity thereof is reduced, theluminosity contrast can be added to the chromaticity contrast in thepseudo color image.

Note that for cases in which a luminosity display gradation is assignedto the multiplied reflectance image or either of the two multipliedfluorescence images, because the gain changes by a large amount if thedistance between the target subject and the image obtaining meanschanges a large amount, the brightness of the displayed pseudo colorimage also changes by a corresponding large amount. Therefore, byassigning a luminosity display gradation to the reflectance image oreither of the two fluorescence images prior to the multiplication of thegain therewith, a large change in the brightness of the pseudo colorimage can be prevented.

Further, by expanding the dynamic range of the multiplied reflectanceimage data and/or the dynamic range of both of the multipliedfluorescence image data, so that the dynamic range of the multipliedreflectance image data and/or the dynamic range of both of themultiplied fluorescence image data spans substantially the entiredynamic range of the display means, because the contrast of themultiplied reflectance image or the multiplied fluorescence image can beexpanded, the change in the tissue state of the target subject appearingin the pseudo color image can be represented in detail, whereby thedistinguishability of the tissue state of the target subject can beimproved.

Note that in this case, by switching, by use of a switching means, thedynamic range expanding means between a drive mode and a non-drive mode,because the dynamic range expansion process can be set so as to not beperformed in cases in which said process is not required, a pseudo colorimage reflecting the preferences of the operator can be displayed.

Further, by making the statistical quantity consist of at least one ofthe following elements of the fluorescence image data or the reflectanceimage data: the maximum value, the minimum value, the average value, avalue combining the maximum value and the standard deviation, a valuecombining the maximum and minimum values, a value combining the minimumvalue and the standard deviation, and a value combining the averagevalue and the standard deviation; the computation of the statisticalquantity can be performed comparatively easily.

Still further, if the gain computing means is a means for computing thegain based on the statistical quantity of the fluorescence image data orthe reflectance image data within a desired portion of the fluorescenceimage data or the reflectance image data, the amount of computationrequired for computing the statistical quantity can be reduced.

In addition, although the change in the intensity of the fluorescentlight emitted from a diseased portion is in-phase in both multipliedfluorescence image data, by obtaining a reverse fluorescent image databy inverting the intensity of either of the two multiplied fluorescenceimage data, the change in intensity between the reverse fluorescenceimage data and the other of the two multiplied fluorescence image data,can be made to be antiphase. Accordingly, the change between the hue ofthe diseased portion and the hue of the normal portion appearing in thepseudo color image can be enlarged, whereby the distinguishability ofthe tissue state of the target subject can be improved a level.

Note that for cases in which the intensity has been inverted, there arecases in which the dark portions other that the diseased portionincluded in the pseudo color image become the same color as the diseasedportion. Therefor, by multiplying the multiplied fluorescent image ofwhich the intensity has been inverted by a constant, the effect wherebythe dark portions appearing in the pseudo color image become the samecolor as the diseased portion can be suppressed, whereby themisrecognition of the diseased portion and the portions that are simplydark portions can be prevented, and the distinguishability of the tissuestate of the target subject can be improved a level.

Further, in the case that a bit shifting means is provided for shiftingthe bits of the reflectance image data or the fluorescence image datafor cases in which the fluorescence image data or the reflectance datais represented by data constituted of 9 bits or more, so that said datais expressed by the lower 8 bits thereof, and the gain computing meansis a means for computing the gain based on the statistical quantity ofthe bit-shifted data, a common 8-bit calculator can be employed and theprocessing speed can be increased.

Still further, if a GaN type semiconductor laser is employed as theexcitation light source, the light source can be provided as a compactand low-cost light source; further, if the wavelength band thereof is inthe range from 400–420 nm, the fluorescent light can be caused to begenerated efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the first embodiment of a fluorescentendoscope implementing the fluorescence image display apparatusaccording to the present invention,

FIG. 2 is a schematic drawing of the optical transmitting filterutilized in the fluorescent endoscope according to the first embodiment(the first thereof),

FIG. 3 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the firstembodiment of the present invention,

FIG. 4 is a drawing illustrating the multiplied of the gain,

FIG. 5 is a graph showing the display gradation curves of G and R,

FIG. 6 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the secondembodiment of the present invention,

FIGS. 7A and 7B are graphs illustrating the intensity inversion,

FIG. 8 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the thirdembodiment of the present invention,

FIG. 9 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the fourthembodiment of the present invention,

FIGS. 10A and 10B are graphs illustrating the dynamic range expansionprocess,

FIG. 11 is a drawing of the state in which the fluorescent endoscopeaccording to the fourth embodiment has been provided with a foot switchor a hand operated switch,

FIG. 12 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the fifthembodiment of the present invention,

FIG. 13 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the sixthembodiment of the present invention,

FIG. 14 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the seventhembodiment of the present invention,

FIG. 15 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the eighthembodiment of the present invention,

FIG. 16 is a schematic drawing of the optical transmitting filterutilized in the fluorescent endoscope according to the eighth embodiment(the second thereof),

FIG. 17 is a drawing illustrating the computation of the gain,

FIG. 18 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the ninthembodiment of the present invention,

FIG. 19 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the tenthembodiment of the present invention,

FIG. 20 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the eleventhembodiment of the present invention,

FIG. 21 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the twelfthembodiment of the present invention,

FIG. 22 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the thirteenthembodiment of the present invention,

FIG. 23 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the fourteenthembodiment of the present invention,

FIG. 24 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the fifteenthembodiment of the present invention,

FIG. 25 is a schematic block diagram of the configuration of the imagecomputing unit of the fluorescent endoscope according to the sixteenthembodiment of the present invention, and

FIG. 26 is a drawing illustrating the intensity distributions of thefluorescent light spectra of a tissue in the diseased state and of atissue in the normal state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter the preferred embodiments of the present invention will beexplained with reference to the attached drawings. FIG. 1 is a schematicdrawing a fluorescent endoscope implementing the fluorescence imagedisplay apparatus according to first embodiment of present invention.

The fluorescent endoscope according to the first embodiment comprises:an endoscope insertion portion 100 to be inserted into the primary nidusand areas of suspected secondary infection of a patient; an image dataprocessing portion 1 for outputting as image data the data obtained of aliving tissue (hereinafter referred to as a target subject); and amonitor 600 for displaying the image data outputted from the image dataprocessing portion 1 as a visible image.

The image data processing portion 1 comprises: an illuminating unit 110provided with two light sources for emitting a white light Lw forobtaining a standard image (a reflectance image) and an excitation lightLr for obtaining a fluorescence image, respectively; an image detectingunit 300 for obtaining a fluorescence image Zj, which is formed of thefluorescent light emitted from a target subject 50 upon the irradiationthereof by the excitation light Lr, and a reflectance image Zs, which isformed of the light reflected from the target subject 50 upon theirradiation thereof by the white light Lw containing a reference lightLs, and converting said obtained fluorescence image Zj and reflectanceimage Zs to respective digital values and outputting said digital valuesas respective image data; an image computing unit 400 for subjecting theimage data of the fluorescence image outputted from the image detectingunit 300 to computational processes and outputting a pseudo color imagedata; a display signal processing unit 500 for converting a standardimage to digital values to obtain an image data thereof, and convertingsaid image data and the pseudo color image data outputted from the imagecomputing unit 400 to video signals and outputting said video signals;and a control computer 200 for controlling the operation of each unit.Note that according to the first embodiment, the obtainment of areflectance image Zs is not performed.

The endoscope insertion portion 100 is provided with a light guide 101extending internally to the distal end thereof, a CCD cable 102, and animage fiber 103. An illuminating lens 104 and an objective lens 105 areprovided at the distal end portion of the light guide 101 and the CCDcable 102, that is, at the distal end of the endoscope insertion portion100. Further, the image fiber 103 is formed of a composite glass fiber,and a focusing lens 106 is provided at the distal end portion thereof. Astandard image obtaining element 107 is connected to the distal endportion of the CCD cable 102, and a reflective prism 108 is attached tothe standard image obtaining element 107. The light guide 101 consistsof a bundled excitation light guide 101 a, which is formed of quartzglass fiber, and white light guide 101 b, which is formed of compositeglass fiber, in the form of an integrated cable; the excitation lightguide 101 a and the white light guide 101 b are connected to theilluminating unit 110. One end of the CCD cable 102 is connected to theimage signal processing unit 500, and one end of the image fiber 103 isconnected to the image detecting unit 300. Note that although not shownin the drawing, the distal end portion of the light guide 101 is formedas two eyelets.

The illuminating unit 110 comprises: a GaN type semiconductor laser 111that emits an excitation light Lr for obtaining fluorescence images; asemiconductor laser power source 112 electrically connected to the GaNtype semiconductor laser 111; an excitation light focusing lens 113 forfocusing the excitation light emitted from the GaN type semiconductorlaser 111; a white light source 114 that emits a white light Lw forobtaining standard images; a white light source power source 115electrically connected to the white light source 114; and a white lightfocusing lens 116 for focusing the white light emitted from the whitelight source 114. Further, because the white light Lw emitted from thewhite light source 114 contains light within the wavelength band thatcan be used as the reference light Ls, the white light source 114 canalso be employed as the reference light source described below.

The image detecting unit 300 comprises: a collimator lens 301 thatfocuses a fluorescence image conveyed thereto via the image fiber 103;an excitation light cutoff filter 302 that cuts off light having awavelength near that of the excitation light from the fluorescenceimage; an optical transmitting filter 303 that extracts light within adesired wavelength band from the fluorescence image transmitted by theexcitation light cutoff filter 302; a filter rotating means 304 forrotating the optical transmitting filter 303; a fluorescent lightfocusing lens 305 for focusing the fluorescence image transmitted by theoptical transmitting filter 303; a high-sensitivity fluorescent imageobtaining element 306 for obtaining the fluorescent image focused by thefluorescent light focusing lens 305; and an AD converter 307 forconverting the fluorescence image obtained by high-sensitivityfluorescent image obtaining element 306 to digital values to obtainimage data thereof.

As shown in FIG. 2, the optical transmitting filter 303 comprises twotypes of band pass filters: a band pass filter 303 a and a band passfilter 303 b. The band pass filter 303 a is a band pass filter thattransmits a fluorescence image formed of light having wavelengths withinthe 430–730 nm wide wavelength band; the band pass filter 303 b is aband pass filter that transmits a fluorescence image formed of lighthaving wavelengths within the 430–530 nm narrow wavelength band.Therefore, according to the image detecting unit 300: a fluorescentimage data representing a wide band fluorescent image is obtained by useof a wide-band band pass filter 303 a, and a fluorescent image datarepresenting a narrow band fluorescent image is obtained by use of anarrow-band band pass filter 303 b.

FIG. 3 is a schematic block diagram of the configuration of the imagecomputing unit 400. As shown in FIG. 3, the image computing unit 400comprises: a fluorescent image memory 401 that stores the wide bandfluorescent image data WS and the narrow band fluorescent image data NSthat has been obtained by the image processing unit 300; a bit shiftingmeans 402 for shifting the data of each pixel value among the pixelvalues of the wide band fluorescent image represented by the wide bandfluorescent image data WS stored in the fluorescent image memory 401that is constituted by nine bits or more so that each of said data isrepresented by eight bits of data or less; a statistical quantitycomputing means 403 provided with an 8-bit statistical quantitycalculator for computing the statistical quantity of the wide bandfluorescent image data WS outputted from the bit shifting means 402; again computing means 404 for computing, based on the statisticalquantity outputted from the statistical quantity computing means 403, again g that the wide band fluorescent image data WS and the narrow bandfluorescent image data NS are to be multiplied by; a gain multiplyingmeans 405 for multiplying the wide band fluorescent image data WS andthe narrow band fluorescent image data NS by the gain g obtained by thegain computing means 404 to obtain a wide band fluorescent image dataWS′ and a narrow band fluorescent image data NS′, which have beenmultiplied by the gain g; a color gradation assigning means 406 forassigning a green (G) color gradation to the wide band fluorescent imagedata WS′ outputted from the gain multiplying means 405; a colorgradation assigning means 407 for assigning a red (R) color gradation tothe narrow band fluorescent image data NS′ outputted from the gainmultiplying means 405; and an image composing means 408 for colorizingand synthesizing the wide band fluorescent image data WS′ and the narrowband fluorescent image data NS′ outputted from the color gradationassigning means 406 and 407, respectively, to obtain a composite imagedata CS representing a composite image.

Note that according to the current embodiment, the wide band fluorescentimage data WS and the narrow band fluorescent image data NS have bothbeen stored in the fluorescent image memory 401; however, each can bestored in respective separate memories.

The display signal processing unit 500 comprises: an AD converter 501that digitizes the visible image signal obtained by the standard imageobtaining element 107 to obtain a standard image data; a standard imagememory 502 that stores the standard image data; and a video signalprocessing circuit 503 that converts the standard image data outputtedby the standard image memory 502 and the composite-image image dataoutputted from the image composing means 408 to video signals andoutputs said video signals.

The monitor 600 is provided with a standard image monitor 601 and acomposite image monitor 602.

Next, the operation of the fluorescent endoscope according to the firstembodiment of the configuration described above will be explained. Inorder to obtain two fluorescence images, each formed of a mutuallydifferent wavelength band of fluorescent light, first, based on a signaloutputted from the control computer 200, the semiconductor laser powersource 112 is activated, and the GaN type semiconductor laser 111 emitsexcitation light Lr having a wavelength of 410 nm. The excitation lightLr emitted by the GaN type semiconductor laser 111 is transmitted by anexcitation light focusing lens 113 and enters the excitation light guide101 a; after being guided to the distal end of the endoscope insertionportion 100, said excitation light Lr passes through the illuminatinglens 104 and is projected onto the target subject 50.

The fluorescence image Zj formed of the fluorescent light emitted fromthe target subject 50 upon the irradiation thereof by the excitationlight Lr is focused by the focusing lens 106, enters the distal end ofthe image fiber 103, and enters the excitation light cutoff filter 302via the image fiber 103. The fluorescent image Zj that has passedthrough the excitation light cutoff filter 302 enters the opticaltransmitting filter 303. Note that the excitation light cutoff filter302 is a long pass filter that transmits all fluorescent light having awavelength of 420 nm or longer. Because the wavelength of the excitationlight is 410 nm, the excitation light reflected from the target subject50 is cutoff by this excitation light cutoff filter 302, and does notenter the optical transmitting filter 303.

The filter rotating means 304 is driven based on a signal from thecontrol computer 200, and after the fluorescent image Zj has passedthrough the band pass filter 303 a, said fluorescent image Zj is focusedby the fluorescent light focusing lens 305 and obtained as a wide bandfluorescent image by the high sensitivity fluorescence image obtainingelement 306. Further, after the fluorescent image Zj has passed throughthe bandpass filter 303 b, said fluorescent image Zj is focused by thefluorescent light focusing lens 305 and obtained as a narrow bandfluorescent image by the high sensitivity fluorescence image obtainingelement 306. The visible image signal from the high sensitivityfluorescence image obtaining element 306 is inputted to the AD converter307, and after being digitized therein, is stored as a wide bandfluorescent image data WS and a narrow band fluorescent image data NS inthe fluorescent image memory 401. Note that the wide band fluorescentimage data WS obtained by the high sensitivity fluorescence imageobtaining element 306 is stored within a wide band fluorescent imageregion (not shown) of the fluorescent image memory 401, and the narrowband fluorescent image data WS obtained by the high sensitivityfluorescence image obtaining element 306 is stored within a narrow bandfluorescent image region (not shown).

The wide band fluorescent image data WS stored in the fluorescent imagememory 401 is inputted to the statistical quantity computing means 403after being bit shifted by the bit shifting means 402 so as to berepresented by an 8-bit data. The statistical quantity computing means403 computes the average value m and the standard deviation σ of eachpixel of the wide band fluorescent image represented by the wide bandfluorescent image data WS. Then, the average value m and the standarddeviation Ca are inputted to the gain computing means 404, and the gaing is computed according to the above described Formula (2). Note thatthe maximum and minimum values of each pixel value of the wide bandfluorescent image can be obtained, and the gain g computed according tothe above described formula (1). Further, the gain g can be computedbased the average value m and the standard deviation σ computed of onlythe pixels included within a desired region within the fluorescent image(e.g., an image region having a particularly high level of interest).

The computed gain g is inputted to the gain multiplying means 405, andthe gain multiplying means 405 multiplies the wide band fluorescentimage data WS and the narrow band fluorescent image data NS by theinputted gain g. Note that the gain g that the wide band fluorescentimage data WS and the narrow band fluorescent image data NS aremultiplied by can be the same value; however, different values having aconstant relationship may also be used.

The wide band fluorescent image data WS′ which has been multiplied bythe gain g is inputted to the color gradation assigning means 406, andthe color gradation assigning means 406 assigns a G color gradationthereto. Further, the narrow band fluorescent image data NS′ which hasbeen multiplied by the gain g is inputted to the color gradationassigning means 407, and the color gradation assigning means 407 assignsan R color gradation thereto.

Here, as shown in FIG. 4, for a case in which the distribution of thepixel values of the wide band fluorescent image data WS and the narrowband fluorescent image data NS have a distribution such as thatindicated by 10, 10′ in the graph, by multiplying the gain g into thewide band fluorescent image data WS and the narrow band fluorescentimage data NS, the distribution range of the pixel values thereof can beshifted to the high pixel value side of the graph, as indicated by 20,20′ in the graph. Then, based on the pixel value distribution rangeindicated by 20, 20′ in the graph of FIG. 4, a G and R color gradationare assigned to the wide band fluorescent image data WS′ and the narrowband fluorescent image data NS′, respectively, according to thegradation process function shown in FIG. 5, for example.

The wide band fluorescent image data WS′ and the narrow band fluorescentimage data NS′ to which G and R color gradation are assigned to,respectively, are inputted to the image composing means 408; the imagecomposing means 408 colorizes and synthesizes the image data NS′ and WS′to obtain a composite image data CS representing a composite image.

The composite image data CS is inputted to the video signal processingcircuit 503, and after being DA converted therein, is inputted to themonitor unit 600 and displayed as a composite image on the compositeimage monitor 602. Here, normal tissue appearing in the composite imagedisplayed on the composite image monitor 602 is shown by a brightyellow-green color, and diseased tissue appearing therein is shown by adark green color.

Next, the operation occurring when a standard image is to be displayedwill be explained. When a standard image is to be displayed, first,based on a control signal from the control computer 200, the white lightsource power source 115 is activated and white light Lw is emitted fromthe white light source 114. The white light Lw enters the white lightguide 101 b via the white light focusing lens 116, and after beingguided to the distal end of the endoscope insertion portion 100, saidwhite light Lw is emitted onto the target subject 50 from theilluminating lens 104. The light reflected from the target subject 50upon the irradiation thereof by the white light Lw is focused by theobjective lens 105, reflected by the reflective prism 108, and focusedonto the standard image obtaining element 107. The visible image signalobtained by the standard image obtaining element 107 is inputted to theAD converter 501, and after being digitized therein, is stored as astandard image data in the standard image memory 502. The standard imagedata stored in the standard image memory 502 is inputted to the videosignal processing circuit 503, and after being DA converted therein, isinputted to the monitor unit 600 and displayed as a visible image on thestandard image monitor 601.

The continuous operations occurring when a composite image or a standardimage is to be obtained are controlled by the control computer 200.

According to the above described endoscope implementing the fluorescenceimage obtaining apparatus according to the first embodiment of thepresent invention: a statistical quantity computing means 403 forcomputing the statistical quantity of the distribution of the pixelvalues of a wide band fluorescent image represented by a wide bandfluorescence image data WS is provided; because the gain g is computedbased on said statistical quantity and the wide band fluorescence imagedata WS and the narrow band fluorescence image data NS are multiplied bysaid gain, regardless of the intensity of the fluorescent light emittedfrom the target subject 50, a composite image data CS formed from a wideband fluorescence image data WS and a narrow band fluorescence imagedata NS having a desired pixel value can be obtained, and the compositeimage can be made to have a desired luminosity. That is to say, theluminosity of the fluorescence image, which is an effect of theintensity of the fluorescent light, can be adjusted so as to be within adesired range, whereby the distinguishability of the tissue state of thetarget subject can be improved.

Further, because the statistical quantity has been taken as acombination of the average value m and the standard deviation σ of thedistribution of the pixel values of the wide band fluorescence imagedata WS, the computation of the statistical quantity can be performedcomparatively easily, and an appropriate display gradation can beassigned.

Still further, for cases in which the statistical quantity computingmeans 403 is a means for computing the statistical quantity from adesired region of a reflectance image, the amount of computationrequired can be reduced.

In addition, because a bit shifting means 402 has been provided forshifting the data of the pixel values of the wide band fluorescenceimage data WS for cases in which said pixel values are represented bynine or more bits of data, so that said data is constituted of eightbits of data, and the statistical quantity computing means 403 is ameans for computing the statistical quantity based on the bit shifteddata, a common 8-bit calculator can be used as the statistical quantitycomputing means 403, and the speed with which the computationalprocesses are performed can be increased.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the second embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the secondembodiment: the image computing unit 400 of the first embodiment invertsthe intensity of the narrow band fluorescent image data NS′, which hasbeen multiplied by the gain g, to obtain a reverse narrow bandfluorescent image data NS″; and assigns a R color gradation is to thereverse narrow band fluorescent image data NS″. Therefore, as shown inFIG. 6, the image computing unit 400 of the endoscope according to thesecond embodiment is provided with an intensity inverting means 410 forinverting the intensity of the narrow band fluorescent image data NS′,which has been multiplied by the gain g.

The intensity inverting means 410 subtracts, for cases in which thenarrow band fluorescent image data NS′ is represented by 8-bit data,each pixel value of the fluorescent image represented by the narrow bandfluorescent image data NS′ from 255 to obtain a subtraction value; thissubtraction value is taken as the pixel value of the pixels of thefluorescent image of which the intensity has been inverted. Note thatinstead of subtracting from 255, the reciprocal of the pixel values(i.e., the 1/pixel value) can be taken as the pixel values of thefluorescent image of which the intensity has been inverted.

Hereinafter the operation of the second embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe second embodiment: the gain g is computed based on the wide bandfluorescence image data WS; the narrow band fluorescent image data NS ismultiplied by the gain g to obtain a narrow band fluorescent image dataNS′; the narrow band fluorescent image data NS′ is inputted to theintensity inverting mean 410; the intensity inverting means 410 invertsthe intensity of the narrow band fluorescent image data NS′ to obtain areverse narrow band fluorescent image data NS″, assigns an R colorgradation to the reverse narrow band fluorescent image data NS″, andthen combines the reverse narrow band fluorescent image data NS″ and thewide band fluorescence image data WS′, to which a green color gradationhas been assigned, to obtain a composite image data CS.

Here, the effect of the inversion of the intensity will be explained.FIG. 7 is a graph illustrating the effect of the intensity inversion. Asshown in FIG. 7A, if a two-dimensional colorized space having ahorizontal axis G and a vertical axis R is considered, before theinversion of the intensity is performed, because the ratio of the wideband fluorescence image data WS′ and the narrow band fluorescence imagedata NS′ of the normal tissue is such that the wide band fluorescenceimage data WS′ side is slightly larger, the normal tissue is shown as abright yellow-green color in the composite image. On the other hand, theintensity of the diseased portion is reduced, and in comparison to thenormal tissue, because the ratio of the wide band fluorescence imagedata WS′ and the narrow band fluorescence image data NS′ of the normaltissue is such that value of the wide band fluorescence image data WS′is larger, opposed to that of the narrow band fluorescence image dataNS′; accordingly, the diseased tissue is shown as a dark green color inthe composite image. In this manner, although the normal tissue and thediseased tissue are shown as a greenish yellow color and a dark greencolor, respectively, in the composite image, because the difference inthe hue contrast is slight, there are cases in which it is difficult todistinguish between the normal tissue and the diseased tissue.

In contrast to this, as shown in FIG. 7B, if the intensity of the narrowband fluorescent image data NS′ is inverted, because the changeoccurring in the intensity of the fluorescent light emitted from thediseased tissue occurs as an reverse phase change in the wide bandfluorescence image data WS′ and the narrow band fluorescence image dataNS′, the value of the narrow band fluorescent image data NS′ becomeslarger than that of the wide band fluorescence image data WS′.Therefore, the normal tissue is shown as a bright green color and thediseased tissue as a bright red color, and the difference between thehue contrast of the normal tissue and the diseased tissue becomesenlarged in comparison to the state prior to the inversion of theintensity of the narrow band fluorescent image data NS′. Therefore,according to the second embodiment described above, by inverting theintensity of the narrow band fluorescent image data NS′, the differencebetween the normal tissue and the diseased tissue appearing in thecomposite image can be rendered more clearly, whereby thedistinguishability of the tissue state of the target subject can beimproved a level.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the third embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the thirdembodiment: the image computing unit 400 of the second embodimentinverts the intensity of the narrow band fluorescent image data NS′,which has been multiplied by the gain g, to obtain a reverse narrow bandfluorescent image data NS″; then, multiplies the reverse narrow bandfluorescent image data NS″ by a predetermined constant α (α>1) to obtaina constant-multiplied reverse narrow band fluorescence image NS″; andassigns a R color gradation to the constant-multiplied reverse narrowband fluorescent image data NS″, which has been multiplied by theconstant α. Therefore, as shown in FIG. 8, the image computing unit 400of the endoscope according to the third embodiment comprises: anintensity inverting means 410 for inverting the intensity of the narrowband fluorescent image data NS′, which has been multiplied by the gaing, to obtain a reverse narrow band fluorescent image data NS″; and aconstant multiplying means 412 for multiplying the reverse narrow bandfluorescent image data NS″ by a predetermined constant α to obtain aconstant-multiplied reverse narrow band fluorescent image data NS″.

Hereinafter the operation of the third embodiment will be explained.Note that because the processes up until the multiplication thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe third embodiment: the gain g is computed based on the wide bandfluorescence image data WS; the narrow band fluorescent image data NS ismultiplied by the gain g to obtain a narrow band fluorescent image dataNS′; the narrow band fluorescent image data NS′ is inputted to theintensity inverting mean 410; and the intensity inverting means 410inverts the intensity of the narrow band fluorescent image data NS′ toobtain a reverse narrow band fluorescent image data NS″. Then, thereverse narrow band fluorescent image data NS″ is inputted to theconstant multiplying means 412, and the constant multiplying means 412multiplies the reverse narrow band fluorescent image data NS″ by apredetermined constant α to obtain a constant-multiplied reverse narrowband fluorescent image data NS″. An R color gradation is assigned to thenarrow band fluorescence image data NS″, which has been multiplied bythe constant α, a G color gradation is assigned to the wide bandfluorescence image data WS′, then the two are combined to form acomposite image data CS.

In the case that the narrow band fluorescence data NS′ is intensityinverted, the dark portions included in the composite image other thandiseased tissue also become red in color, thereby making ambiguous thedifference between diseased tissue and these dark portions. Therefore,according to the third embodiment, the constant multiplying means 412multiplies a constant α to the narrow band fluorescence data NS′, whichhas been intensity inverted, whereby the effect causing the darkportions occurring in the composite image to also become red in colorcan be suppressed, preventing the misrecognition of the diseased tissueand the portions that are simply dark, and thereby improving thedistinguishability of the tissue state by a level.

Note that according to the second and third embodiments, although theintensity of the narrow band fluorescent image data NS′ has beeninverted, the intensity of the wide band fluorescence image data WS maybe inverted instead.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the fourth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the fourthembodiment: the image computing unit 400 of the first embodimentsubjects the narrow band fluorescent image data NS′ and the wide bandfluorescent image data WS′, which have been multiplied by the gain g, toa dynamic range expansion process, based on the statistical quantitycomputed by the statistical quantity computing means 403. Therefore, asshown in FIG. 9, the image computing unit 400 of the endoscope accordingto the fourth embodiment is provided with a dynamic range expandingmeans 414 for subjecting the narrow band fluorescent image data NS′ andthe wide band fluorescent image data WS′ to a dynamic range expansionprocess.

As shown in the Formula (3) below, the dynamic range expanding means 414computes, based on the average value m and the standard deviation σ ofeach pixel of the wide band fluorescent image computed by thestatistical quantity computing means 403, the distribution range of thepixel values of each fluorescence image represented by the wide bandfluorescence image data DWS′ and the narrow band fluorescent image dataDNS′, which have been subjected to the dynamic range expansion process.Note that in the Formula (3), b=2, for example.Distribution range=m−b×σ to m+b×σ  (3)

Then, if the minimum value (Min) is designated as m−b×σ, the maximumvalue (Max) as m+b×σ, each pixel value of each fluorescent image thathas been subjected to the dynamic range expansion process can becomputed by use of the function g (x) (where x equals the pixel valuesof the narrow band fluorescent image and the wide band fluorescent imagewhich have been multiplied by the gain g) shown in the Formula (4)below.g(x)=(x−Min)/(Max−Min)  (4)

Hereinafter the operation of the fourth embodiment will be explained.Note that because the processes up until the multiplication of the gaing into the fluorescent image data are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe fourth embodiment: the gain g is computed based on the wide bandfluorescence image data WS; the narrow band fluorescent image data NSand the wide band fluorescence image data WS are multiplied by the gaing to obtain a narrow band fluorescent image data NS′ and a wide bandfluorescence image data WS′, which have been multiplied by the gain g;the narrow band fluorescent image data NS′ and the wide bandfluorescence image data WS′ are inputted to the dynamic range expandingmeans 414, and are subjected to the dynamic range expansion processtherein to obtain a the wide band fluorescence image data DWS′ and anarrow band fluorescent image data DNS′. The wide band fluorescenceimage data DWS′ and the narrow band fluorescent image data DNS′ areassigned an R color gradation and a G color gradation, respectively, andare then combined to obtain a composite image data CS.

Here, as shown in FIG. 10A, for cases in which the distribution of thepixel values of the wide band fluorescence image and the narrow bandfluorescent image prior to the subjection thereof to the dynamic rangeexpansion process is that indicated by 12, 12′ in the graph, because thedistribution range thereof is present on only a portion of the displaygradation curve 32 of the composite image monitor 602, the contrast ofthe composite image formed thereof would not be very high. In contrastto this, by subjecting the wide band fluorescence image and the narrowband fluorescent image to the dynamic range expansion process, thedistribution range of the pixel values thereof can be made to spansubstantially the entire area of the display gradation curve 32 of thecomposite image monitor 602, as indicated by 14, 14′ in the graph shownin FIG. 14B, whereby the contrast of the composite image formed thereofcan be made higher. Accordingly, the change in the tissue state of thetarget subject 50 can be represented more accurately in the compositeimage, whereby the distinguishability of the tissue state of the targetsubject 50 can be further improved.

Note that for cases in which the statistical quantity computing means403 computes the Max and Min values of each pixel of the wide bandfluorescence image, the dynamic range expanding means 414 can computethe distribution range of the pixel values of each fluorescent imagerepresented by the wide band fluorescence image data DWS′ and the narrowband fluorescent image data DNS′, which have been subjected to thedynamic range expansion process, by use of the Formula (5) below. Notethat in Formula (5), c and d are arbitrary constants.Distribution range=(Max+Min)/2−cX(Max−Min)/2 to(Max+Min)/2+dX(Max−Min)/2  (5)

Further, according to the fourth embodiment, when the normal tissue andthe diseased tissue are adequately interspersed there is no problem;however, for cases in which only normal tissue or only diseased tissueappears in the composite image, if said composite image is subjected tothe dynamic range expansion process, because the change within thetissue state of the normal tissue or within the tissue state of thediseased tissue becomes assigned to the dynamic range of the compositeimage monitor 602, it becomes impossible to discern whether thedisplayed composite image is a normal tissue or a diseased tissue.

Accordingly, the performance of the dynamic range expansion process canalso be performed only at those times desired by the operator of theendoscope. In this case, the dynamic range expansion means 414 can beswitched on and off by a footswitch 210 or a hand held switch 212 asshown in FIG. 11.

Further, according to the fourth embodiment described above, the dynamicrange expanding means 414 has been provided on the first embodiment toperform the dynamic range process; however, it is also possible toperform the same dynamic range expansion process in the second and thirdembodiments. In this case, according to the second embodiment, thedynamic range expansion process can be performed on the reverse narrowband fluorescent image data NS″, which has been obtained by the reversalof the intensity of the narrow band fluorescent image data NS′ by theintensity inverting means 410; in the third embodiment, the dynamicrange expansion process can be performed on the constant-multipliedreverse narrow band fluorescent image data NS″.

Note that according to the first through the fourth embodimentsdescribed above, a G color gradation has been assigned to the wide bandfluorescence image data WS′ (included those of which the dynamic rangehas been expanded) and an R color gradation has been assigned to thenarrow band fluorescent image data NS′ (including those of which thedynamic range has been expanded, those of which the intensity thereofhas been inverted, and those that have been multiplied by the constantα); however, an R color gradation can be assigned to the wide bandfluorescence image data WS′, and a G color gradation can be assigned tothe narrow band fluorescent image data NS′. Further, in addition to theG and R color gradations, a B color gradation may be assigned as well.In this case, a G and a B color gradation can be assigned to the wideband fluorescence image data WS′, and an R color gradation can beassigned to the narrow band fluorescent image data NS′; alternatively, aG and a B color gradation can be assigned to the narrow bandfluorescence image data NS′, and an R color gradation can be assigned tothe wide band fluorescent image data WS′. Note that the change in theassignment of the color gradations may be performed after thefluorescent images have been subjected to the dynamic range expansionprocess, the constant α multiplying process, or the intensity inversionprocess.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the fifth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the fifthembodiment: as in the first embodiment, a hue image data is obtained ofthe narrow band fluorescent image data NS′ and the wide band fluorescentimage data WS′, which has been multiplied by the gain g, and aluminosity image data is obtained of the wide band fluorescent imagedata WS′, and the hue image data and the luminosity image data arecombined to obtain a composite image data. Therefore, as shown in FIG.12, the image computing unit 400 of the endoscope according to the fifthembodiment comprises: a hue image data forming means 420, instead of thehue gradation assigning means 406, the hue gradation assigning means 407and the image composing means 408, for forming a hue data H, whichrepresents a hue, from the narrow band fluorescent image data NS′ andthe wide band fluorescent image data WS′, which has been multiplied bythe gain g; a luminosity image data forming means 422 for forming, basedon the wide band fluorescent image data WS′, a luminosity image data Vrepresenting a brightness; and an image composing means 424 forcombining the hue data H and the luminosity image data V to obtain acomposite image data CS′.

The hue image data forming means 420 outputs the wide band fluorescentimage data WS′ and the narrow band fluorescent image data NS′, which hasbeen multiplied by the gain g, to respectively different color planes(e.g., G, R), and forms, based on the additive color mixture method, acolor added and mixed image data representing a color added and mixedimage then, by computing, based on this color added and mixed imagedata, the hue value, of the color added and mixed image represented bysaid color added and mixed image data, occurring in the Munsell colorsystem, the hue image data forming means 420 forms a hue data value H.

The luminosity image data forming means 422 refers to a prerecordedlook-up table correlating the range of the pixel values of the wide bandfluorescent image which has been multiplied by the gain g represented bythe wide band fluorescent image data WS′ and a luminosity V (Value)occurring in the Munsell color system, and forms a luminosity image dataV.

Hereinafter the operation of the fifth embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe fifth embodiment: the narrow band fluorescent image data NS′ and thewide band fluorescence image data WS′, which has been multiplied by thegain g, are inputted to the hue image data forming means 420. Next, thehue image data forming means 420 outputs the wide band fluorescent imagedata WS′ and the narrow band fluorescent image data NS′ to respectivelydifferent color planes, and forms, based on the additive color mixturemethod, a color added and mixed image data representing a color addedand mixed image ; then, by computing, based on this color added andmixed image data, the hue value of the color added and mixed imagerepresented by said color added and mixed image data and occurring inthe Munsell color system, the hue image data forming means 420 forms ahue data value H.

Meanwhile, the wide band fluorescent image data WS′, which has beenmultiplied by the gain g, is inputted to the luminosity image dataforming means 422; then, the luminosity image data forming means forms,based on the range of the pixel values of the wide band fluorescentimage represented by the wide band fluorescent image data WS′ and thelook-up table, a luminosity image data V determining a luminosity V(Value) occurring in the Munsell color system.

The hue image data H and the luminosity image data V are inputted to theimage composing means 424, and the image composing means 424 forms acomposite image data CS′. In this case, because a saturation is requiredin addition to the hue and luminosity, when the composite image CS′ isto be composed, the largest value of each hue and each luminosity is setas a saturation value S occurring in the Munsell color system, and thecomposite image CS′ is formed by performing an RGB conversion process.The formed composite image CS′ is displayed on the composite imagemonitor 602. Note that the setting of the saturation may alternativelybe set according to the preferences of the operator.

Here, according to the above-described fifth embodiment, by combining ahue image data H is formed from the wide band fluorescent image and thenarrow band fluorescent image with a luminosity image data V to form acomposite image CS′, the hue of the composite image CS′ displayed on thecomposite image monitor 602 becomes a hue that reflects the tissue stateof the target subject 50, and the luminosity reflects the form of thetarget subject 50. Accordingly, data relating to the tissue state of thetarget subject 50 as well as data relating to the form of the targetsubject 50 can be displayed concurrently in a single image.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the sixth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the sixthembodiment: the narrow band fluorescent image data NS′ and the wide bandfluorescent image data WS′, which have been multiplied by the gain g, asin the fifth embodiment, are subjected to a dynamic range expansionprocess, based on the statistical quantity computed by the statisticalquantity computing means 403. Therefore, as shown in FIG. 13, the imagecomputing unit 400 of the endoscope according to the sixth embodiment isprovided with a dynamic range expanding means 426 for subjecting thewide band fluorescent image data WS′, which has been multiplied by thegain g, to a dynamic range expansion process. Note that because thedynamic range expanding means 426 performs the same process as thatperformed by the dynamic range expanding means 414 of the fourthembodiment, a detailed explanation thereof has been omitted.

In this manner, by providing the dynamic range expanding means 426,because the distribution of the luminosity image data V can be made tospan substantially the entire area of the display gradation curve of thecomposite image monitor 602, the contrast of the composite image formedthereof can be made higher. Accordingly, the change in the tissue stateof the target subject 50 can be represented more accurately in thecomposite image, whereby the distinguishability of the tissue state ofthe target subject 50 can be further improved.

Note that according to the sixth embodiment, the dynamic expansionprocess can be preset so as to be performed for each image, or can beperformed only when so desired by the operator of the endoscope, by useof a foot switch 210 or a hand operated switch 212, in the same manneras in the fourth embodiment.

Further, according to the above-described fifth and sixth embodiments,although hue image data H and luminosity image data V have been formedin addition to the processes performed in the first embodiment, it isalso possible that a hue image data H and luminosity image data V beformed and combined to obtain a composite image data CS′ in the secondthrough fourth embodiments described above. In this case, according tothe second embodiment, the hue image data H can be formed utilizing thereverse narrow band fluorescence image NS″; according to the thirdembodiment, the hue image data H can be formed utilizing theconstant-multiplied reverse narrow band fluorescence image NS″. Further,according to the fourth embodiment, the hue image data H can be formedutilizing the wide band fluorescence image DWS′ and the narrow bandfluorescence image DNS′, which have been subjected to the dynamic rangeexpansion process.

Still further, according to the above-described fifth and sixthembodiments, although the luminosity image data V has been formed, basedon the wide band fluorescent image data WS′, which has been multipliedby the gain g, by the luminosity image data forming means 422, theluminosity image data V may also be formed based on the narrow bandfluorescent image data NS′, which has been multiplied by the gain g.

Note that according to the fifth and sixth embodiments, although the hueimage H (a uniform saturation) has been computed, these embodiments arenot limited thereto: an image corresponding to the the X,Y components ofan XYZ color space; the ab components of a Lab color space; the uvcomponents of a Luv color space; the a*b* components of a uniform La*b*color space; the u*v* components of a uniform Lu*v* color space; etc.can also be computed.

Further, according to the fifth and sixth embodiments, although theluminosity image data V has been formed, based on the wide bandfluorescent image data WS′, which has been multiplied by the gain g, bythe luminosity image data forming means 422, the luminosity image data Vcan be formed based on the wide band fluorescent image data WS, whichhas not yet been multiplied by the gain g, as per the seventh embodimentshown in FIG. 14. In this case, it is preferable that it be possible toswitch the data from which the luminosity image data V is to be formedbetween the image data prior to the multiplication thereof by the gain gor the image data which has been multiplied by the gain g.

Here, in the case of forming the luminosity image data V from the wideband fluorescent image data WS′, which has been multiplied by the gaing, if there is a large amount of variation in the distance between thetarget subject 50 and the distal end of the endoscope insertion portion100, because there is a corresponding large amount of change in thegain, the brightness of the displayed composite image also varies alarge amount. Therefore, by forming the luminosity image data V based onthe wide band fluorescent image data WS, which has not yet beenmultiplied by the gain g, the aforementioned large variations of thebrightness of the displayed composite image can be prevented.

Further, according to the first through the seventh embodimentsdescribed above, although the gain g has been computed based on thestatistical quantity of the wide band fluorescent image data WS, thegain g can also be computed based on the narrow band fluorescent imagedata NS.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the eighth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the eighthembodiment: whereas in the first embodiment the gain is computed basedon the statistical quantity of the wide band fluorescent image data WS,in the eighth embodiment, the gain is computed based upon thestatistical quantity of the reflectance image data RS obtained from thereflectance image Zs formed from the light reflected from the targetsubject 50 upon the irradiation thereof by the reference light Ls.

According to the configuration of the endoscope of the eighthembodiment: the optical transmitting filter 303 of the image detectingunit 300 of the first embodiment is provided as an optical transmittingfilter 701; further, as shown in FIG. 15, the fluorescence image memory401 of the image computing unit 400 is provided as a fluorescentimage/standard image memory 801; further comprising a bit shifting means802 for shifting the number of bits constituting the data of thereflectance image data RS; a statistical quantity computing means 803for computing the statistical quantity of the bit shifted reflectanceimage data RS; and a gain computing means 804 for a computing a gain rgbased on the statistical quantity obtained by the statistical quantitycomputing means 803.

As shown in FIG. 16, the optical transmitting filter 701 is formed ofthree types of band pass filters: 701 a, 701 b, and 701 c. The band passfilter 701 a is a band pass filter for transmitting a wide bandfluorescent image formed of fluorescent light having wavelengths in the430–730 nm wavelength band. The band pass filter 701 b is a band passfilter for transmitting a narrow band fluorescent image formed offluorescent light having wavelengths in the 430–530 nm wavelength band.The bandpass filter 701 c is a band-pass filter for transmitting areflectance image formed of light having wavelengths in the 750–900 nmwavelength band.

Further, the fluorescent image/standard image memory 801 comprises awide band fluorescence image recording region, a narrow bandfluorescence image recording region, and a reflectance image recordingregion: the fluorescence images transmitted by the band pass filters 701a, 701 b are stored in the respective wide band fluorescence imagerecording region and narrow band fluorescence image recording region;and the reflectance image transmitted by the band pass filter 701 c isstored in the reflectance image recording region.

The statistical quantity computing means 803 computes the average valuerm and the standard deviation rσ of each pixel of the reflectance imagerepresented by the reflectance image data RS. Then, the average value rmand the standard deviation rσ are inputted to the gain computing means804, and the gain rg is computed according to the following Formula (6).Gain upper limit=f(DR×a/(rm+b×rσ))  (6)

The function f (x) is a correction function reflecting the intensityratio of the reflected light intensity (i.e., the value of thereflectance image data RS) and the fluorescent light intensity (i.e.,the values of the wide band fluorescence image data WS and the narrowband fluorescence image data NS). FIG. 17 is a graph illustrating therelation of the distance between the target subject 50 and the distalend of the endoscope insertion portion 100 and the intensity of thereflectance and fluorescence images. Because the distal end portion ofthe light guide 101 is formed as two eyelets, the intensity of thereflectance and fluorescence light is reduced non-linearly up until thedistance z from the target subject 50 becomes z0, as shown in FIG. 17;at a distance larger than z0, the intensity of the reflectance andfluorescence light is reduced in inverse proportion to the square of thedistance z. This is due to the fact that although the merging of thelight emitted from two locations occurs according to a gaussiandistribution if the distance z is greater than or equal to z0, for casesin which the distance z is less than z0, the merging of the lightemitted from two locations does not occur according to a gaussiandistribution.

Therefore, for cases in which the gain rg is computed based on thereflectance image data RS, the manner in which the distribution of thepixel values of the fluorescence and reflectance images which have beenmultiplied by said gain rg changes is such that said change differs inaccordance to the length, short or long, of the distance z.

Accordingly, in a case, for example, in which f (x)=px, at locations forwhich the distance is short, the change in distribution becomesexpressed by a variable (e.g., a value that approaches 1 as the distancez becomes shorter); by setting the coefficient p so that it is aconstant at locations for which the distance is long, a gain rg in whichthe change to the correction function due to the distance z is reducedcan be obtained. Note that because it is not possible to detect thedistance z directly, the value of the coefficient p can be determinedbased upon the value of the reflectance image data RS. That is to say,when the data value of the reflectance image data RS is large, thecoefficient p is set as a value close to 1; when the data value issmall, the coefficient p can be a value computed based on the ratio ofthe fluorescent images and the reflectance image.

Note that by obtaining the maximum value (Max) and the minimum value(Min) of each pixel of the wide band fluorescence image, the gain rg mayalso be computed by use of the following equation (7). In addition, thegain rg may be computed based solely on the pixel values for a desiredregion of the reflectance image (e.g., a region of the image thatwarrants observation with particular attention).Gain upper limit=f[DR×a/{(rMax+rMin)/2+b×(rMax−rMin)/2)  (7)

Hereinafter, the operation of the eighth embodiment will be explained.According to the eighth embodiment: the filter rotating means 304 isdriven based on a signal from the control computer 200, and after thefluorescent image Zj has passed through the band pass filter 701 a, saidfluorescent image Zj is focused by the fluorescent light focusing lens305 and obtained as a wide band fluorescent image by the highsensitivity fluorescence image obtaining element 306. Further, after thefluorescent image Zj has passed through the band pass filter 701 b, saidfluorescent image Zj is focused by the fluorescent light focusing lens305 and obtained as a narrow band fluorescent image by the highsensitivity fluorescence image obtaining element 306. The visible imagesignals from the high sensitivity fluorescence image obtaining element306 are inputted to the AD converter 307, and after being digitizedtherein, are stored as a wide band fluorescent image data WS and anarrow band fluorescent image data NS in the respective wide bandfluorescent image recording region and narrow band fluorescent imagerecording region of the reflectance image/fluorescent image memory 801.

On the other hand, when a reflectance image is to be obtained: first,based on a control signal from the control computer 200, the white lightsource power source 115 is activated and white light Lw is emitted. Thewhite light Lw contains reference light Ls having wavelengths from750–900 nm. The white light Lw enters the white light guide 101 b viathe white light focusing lens 116, and after being guided to the distalend of the endoscope insertion portion 100, said white light Lw isemitted onto the target subject 50 from the illuminating lens 104.

The light reflected from the target subject 50 upon the irradiationthereof by the white light Lw is focused by the focusing lens 106,enters the distal end of the image fiber 103, and enters the excitationlight cutoff filter 302 via the image fiber 103. The reflectance imageZs that has passed through the excitation light cutoff filter 302 entersthe optical transmitting filter 303.

The filter rotating means 304 is driven, based on a signal from thecontrol computer 200, and after the reflectance image Zs has passedthrough the band pass filter 701 c, said reflectance image Zs is focusedby the fluorescent light focusing lens 305 and obtained as a standardimage by the high sensitivity fluorescence image obtaining element 306.The visible image signal from the high sensitivity fluorescence imageobtaining element 306 is inputted to the AD converter 307, and afterbeing digitized therein, is stored as a standard image data RS in thereflectance image recording region of the reflectance image/fluorescentimage memory 801.

The standard image data RS stored in the reflectance image/fluorescentimage memory 801 is inputted to the statistical quantity computing means803 after being bit shifted by the bit shifting means 802 so as to berepresented by 8-bit data. The statistical quantity computing means 803computes the statistical quantity. The statistical quantity is inputtedto the gain computing means 804, and the gain computing means 804computes the gain rg based on said statistical quantity. Then, in thesame manner as in the first embodiment, the wide band fluorescent imagedata WS and the narrow band fluorescent image data NS are multiplied bythe gain g to obtain a wide band fluorescent image data WS′ and a narrowband fluorescent image data NS′. Further, a G color gradation isassigned to the wide band fluorescent image data WS′ and an R colorgradation is assigned to the narrow band fluorescent image data NS′;these two colorized wide band fluorescent image data WS′ and narrow bandfluorescent image data NS′ are then combined to obtain a composite imagedata CS.

Here, the intensity of the light reflected from the target subject 50upon the irradiation thereof by the reference light Ls is larger thanthe intensity of the wide band fluorescent light emitted from the targetsubject 50 upon the irradiation thereof by the excitation light.Therefore, the computation of the gain rg, based on the statisticalquantity, can be performed more advantageously in comparison to thefirst embodiment; whereby the distinguishability of the tissue state ofthe target subject 50 appearing in the composite image formed accordingto the current embodiment can be improved a level.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the ninth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the ninthembodiment: the image computing unit 400 of the eighth embodimentinverts the intensity of the narrow band fluorescent image data NS′,which has been multiplied by the gain rg, to obtain a reverse narrowband fluorescent image data NS″ as in the second embodiment; and assignsa R color gradation to the reverse narrow band fluorescent image dataNS″. Therefore, as shown in FIG. 18, the image computing unit 400 of theendoscope according to the ninth embodiment is provided with anintensity inverting means 410 for inverting the intensity of the narrowband fluorescent image data NS′, which has been multiplied by the gainrg.

Hereinafter the operation of the ninth embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain rg are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe ninth embodiment: the gain rg is computed based on the reflectanceimage data RS; the narrow band fluorescent image data NS is multipliedby the gain rg to obtain a narrow band fluorescent image data NS′; thenarrow band fluorescent image data NS′ is inputted to the intensityinverting means 410; the intensity inverting means 410 inverts theintensity of the narrow band fluorescent image data NS′ to obtain areverse narrow band fluorescent image data NS″, assigns an R colorgradation to the reverse narrow band fluorescent image data NS″, andthen combines the reverse narrow band fluorescent image data NS″ and thewide band fluorescence image data WS′, to which a green color gradationhas been assigned, to obtain a composite image data CS.

In this manner, by inverting the intensity of the narrow bandfluorescent image data NS′, the difference between the normal tissue andthe diseased tissue appearing in the composite image can be renderedmore clearly, whereby the distinguishability of the tissue state of thetarget subject can be improved a level.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the tenth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the tenthembodiment: the image computing unit 400 of the ninth embodiment invertsthe intensity of the narrow band fluorescent image data NS′, which hasbeen multiplied by the gain rg, to obtain a reverse narrow bandfluorescent image data NS″; then, multiplies the reverse narrow bandfluorescent image data NS″ by a predetermined constant α (α>1) to obtaina constant-multiplied reverse narrow band fluorescent image data NS″;and assigns a R color gradation to the constant-multiplied reversenarrow band fluorescent image data NS″, which has been multiplied by theconstant ax has been multiplied. Therefore, as shown in FIG. 19, theimage computing unit 400 of the endoscope according to the tenthembodiment comprises a constant multiplying means 412, which is the sameas that of the third embodiment.

Hereinafter the operation of the tenth embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe tenth embodiment: the gain rg is computed based on the reflectanceimage data RS; the narrow band fluorescent image data NS is multipliedby the gain rg to obtain a narrow band fluorescent image data NS′, whichhas been multiplied by the gain rg; the narrow band fluorescent imagedata NS′ is inputted to the intensity inverting mean 410; and theintensity inverting means 410 inverts the intensity of the narrow bandfluorescent image data NS′ to obtain a reverse narrow band fluorescentimage data NS″. Then, the reverse narrow band fluorescent image data NS″is inputted to the constant multiplying means 412. The constantmultiplying means 412 multiplies the reverse narrow band fluorescentimage data NS″ by a predetermined constant α to obtain aconstant-multiplied reverse narrow band fluorescent image data NS″;assigns an R color gradation to the reverse narrow band fluorescentimage data NS″; and combines this colorized constant-multiplied reversenarrow band fluorescent image data NS″ and the wide band fluorescenceimage data WS′, to which a green color gradation has been assigned, toobtain a composite image data CS.

In this manner, by multiplying the reverse narrow band fluorescent imagedata NS″ by a constant α, the effect wherein the dark portions appearingin the composite image also become red in color can be suppressed thesame as in the third embodiment, preventing the misrecognition ofportions that are simply dark and diseased tissue, and improving thedistinguishability of the tissue state by a level.

Note that according to the ninth an tenth embodiments, the intensity ofthe narrow band fluorescent image data NS′ has been inverted; however,the intensity of the wide band fluorescent image data WS′ may beinverted instead.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the eleventh embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the eleventhembodiment: the gain multiplying means 405 multiplies the narrow bandfluorescent image data NS and the reflectance image data RS by the gainrg to obtain a narrow band fluorescent image data NS′ and a reflectanceimage data RS′; computes the difference data between the narrow bandfluorescent image data NS′ and a reflectance image data RS′; then,multiplies the difference data by a predetermined constant α and assignsan R color gradation to the product obtained thereby. Therefore, asshown in FIG. 20, the image computing unit 400 of the endoscopeaccording to the eleventh embodiment comprises a difference datacomputing means for computing the difference data Ssub between thenarrow band fluorescent image data NS′, which has been multiplied by thegain rg, and the reflectance image data RS′, which has been multipliedby the gain rg, and a constant multiplying means 412, which is the sameas that of the third embodiment.

The difference computing means 810 computes the difference between thevalues of the corresponding pixels of the reflectance image representedby the reflectance image data RS′, which has been multiplied by the gainrg, and the fluorescent image represented by the narrow band fluorescentimage data NS′, which has been multiplied by the gain rg, to obtain adifference data Ssub.

Hereinafter the operation of the eleventh embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe eleventh embodiment: the gain rg is computed based on thereflectance image data RS; the reflectance image represented by thereflectance image data RS is multiplied by the gain rg to obtainreflectance image data RS′, the narrow band fluorescent image data NS ismultiplied by the gain rg to obtain narrow band fluorescent image dataNS′; the reflectance image data RS′ and narrow band fluorescent imagedata NS′ are inputted to the difference computing means 810; and thedifference computing means 810 computes difference data Ssub. Further,the constant multiplying means 412 multiplies the difference data Ssubby the constant α to obtain an α Ssub, and assigns an R color gradationto theα Ssub. Next, the R colorized α Ssub and the wide bandfluorescence image data WS′, to which a green color gradation has beenassigned, are combined to obtain a composite image data CS.

In this manner, by computing the Ssub of the reflectance imagerepresented by the reflectance image data RS′, which has been multipliedby the gain rg, and the narrow band fluorescent image data NS′, whichhas been multiplied by the gain rg, the difference between the diseasedtissue and the normal tissue can be more clearly rendered. That is tosay, by adjusting the luminosity of the fluorescence image, which is aneffect of the intensity of the fluorescent light, to within a desiredluminosity range, the distinguishability of the tissue state of thetarget subject can be improved.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the twelfth embodiment of the present inventionwill be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the twelfthembodiment: the narrow band fluorescent image data NS′ and the wide bandfluorescent image data WS′, which have been multiplied by the gain rg,as in the eighth embodiment, are subjected to a dynamic range expansionprocess, based on the statistical quantity computed by the statisticalquantity computing means 803, to obtain a wide band fluorescence imagedata DWS′ and a narrow band fluorescent image data DNS′. Therefore, asshown in FIG. 20, the image computing unit 400 of the endoscopeaccording to the twelfth embodiment is provided with a dynamic rangeexpanding means 814, which is the same as that of the fourth embodiment.

As shown in the formula (8) below, the dynamic range expanding means 814computes, based on the average value m and the standard deviation σ ofeach pixel of the reflectance image computed by the statistical quantitycomputing means 803, the distribution range of the pixel values of eachfluorescence image represented by the wide band fluorescence image dataDWS′ and the narrow band fluorescent image data DNS′, which have beensubjected to the dynamic range expansion process. Note that in theFormula (8), b=2, for example.Distribution range=rm−b×rσ to rm+b×rσ  (8)

Then, if the minimum value (Min) is designated as rm−b×rσ, the maximumvalue (Max) as rm+b×rσ, each pixel value of each fluorescent image thathas been subjected to the dynamic range expansion process can becomputed by use of the function rg (x) (where x equals the pixel valuesof the narrow band fluorescent image and the wide band fluorescent imagewhich have been multiplied by the gain rg) shown in the Formula (9)below.rg(x)=(x−Min)/(Max−Min)  (9)

Hereinafter the operation of the twelfth embodiment will be explained.Note that because the processes up until the multiplication of thefluorescent image data by the gain g are the same as those of the firstembodiment, further explanation thereof has been omitted. According tothe twelfth embodiment: the gain g is computed based on the reflectanceimage data RS; the narrow band fluorescent image data NS and the wideband fluorescence image data WS are multiplied by the gain g to obtain anarrow band fluorescent image data NS′ and a wide band fluorescenceimage data WS′; the narrow band fluorescent image data NS′ and the wideband fluorescence image data WS′ are inputted to the dynamic rangeexpanding means 814, and are subjected to the dynamic range expansionprocess therein to obtain a the wide band fluorescence image data DWS′and a narrow band fluorescent image data DNS′. The wide bandfluorescence image data DWS′ and the narrow band fluorescent image dataDNS′ are assigned an R color gradation and a G color gradation,respectively, and are then combined to obtain a composite image data CS.

In this manner, by expanding the dynamic range of the narrow bandfluorescent image data NS′ and the wide band fluorescent image data WS′,because the contrast of the composite image formed thereof can be madehigher, the change in the tissue state of the target subject 50 can berepresented more accurately in the composite image, whereby thedistinguishability of the tissue state of the target subject 50 can befurther improved.

Note that for cases in which the statistical quantity computing means803 computes the Max and Min values of each pixel of the reflectanceimage, the dynamic range expanding means 814 can compute thedistribution range of the pixel values of each respective dynamic-rangeexpanded fluorescent image represented by the wide band fluorescenceimage data DWS′ and the narrow band fluorescent image data DNS′, by useof the Formula (10) below. Note that in Formula (10), c and d arearbitrary constants.Distribution range=(rMax+rMin)/2−cX(rMax−rMin)/2 to(rMax+rMin)/2+dX(rMax−rMin)/2  (10)

Note that according to the twelfth embodiment, the dynamic expansionprocess can be preset so as to be performed for each image, or can beperformed only when so desired by the operator of the endoscope, by useof a foot switch 210 or a hand operated switch 212, in the same manneras in the fourth embodiment.

Further, according to the twelfth embodiment described above, thedynamic range expanding means 814 of the eighth embodiment has beenprovided, and the dynamic range process performed; however, it is alsopossible to perform the same dynamic range process in the ninth throughthe eleventh embodiments. In this case, according to the ninthembodiment, the dynamic range expansion process can be performed on thereverse narrow band fluorescent image data NS″; in the tenth embodiment,the dynamic range expansion process can be performed on theconstant-multiplied reverse narrow band fluorescent image data NS″.Further, according to the eleventh embodiment, the dynamic rangeexpansion process can be performed on the constant-multiplied differencedata a Ssub.

Note that according to the eighth through the twelfth embodimentsdescribed above, a G color gradation has been assigned to the wide bandfluorescence image data WS′ (included those of which the dynamic rangehas been expanded) and an R color gradation has been assigned to thenarrow band fluorescent image data NS′ (included those of which thedynamic range has been expanded, those of which the intensity thereofhas been inverted, and those that have been multiplied by the constantα)or to the constant-multiplied difference data α Ssub; however, an Rcolor gradation can be assigned to the wide band fluorescence image dataWS′, and a G color gradation can be assigned to the narrow bandfluorescent image data NS′ or the constant-multiplied difference data αSsub. Further, in addition to the G and R color gradations, a B colorgradation maybe assigned as well. In this case, a G and a B colorgradation can be assigned to the wide band fluorescence image data WS′,and an R color gradation can be assigned to the narrow band fluorescentimage data NS′ or the constant-multiplied difference data a Ssub;alternatively, a G and a B color gradation can be assigned to the narrowband fluorescence image data NS′ or the constant-multiplied differencedata α Ssub, and an R color gradation can be assigned to the wide bandfluorescent image data WS′. Note that the change in the assignment ofthe color gradations can be performed after the fluorescent images andthe constant-multiplied difference data α Ssub have been subjected tothe dynamic range expansion process, the of the constant amultiplication process, or the intensity inversion process.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the thirteenth embodiment of the presentinvention will be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the thirteenthembodiment: a hue image data H is obtained of the narrow bandfluorescent image data NS′ and the wide band fluorescent image data WS′,which have been multiplied by the gain rg, as in the eighth embodiment,a luminosity image data V is obtained of the wide band fluorescent imagedata WS′, and the hue image data H and the luminosity image data V arecombined to obtain a composite image data. Therefore, as shown in FIG.22, the image computing unit 400 of the endoscope according to thethirteenth embodiment comprises, in a configuration similar to that ofthe fifth embodiment: a hue image data forming means 420, instead of ahue gradation assigning means 406, a hue gradation assigning means 407and an image composing means 408, for forming a hue data H, whichrepresents a hue, from the narrow band fluorescent image data NS′ andthe wide band fluorescent image data WS′, which have been multiplied bythe gain rg; a luminosity image data forming means 422 for forming,based on the wide band fluorescent image data WS′, a luminosity imagedata V representing a brightness; and an image composing means 424 forcombining the hue data H and the luminosity image data V to obtain acomposite image data CS′.

Hereinafter the operation of the thirteenth embodiment will beexplained. Note that because the processes up until the multiplicationof the fluorescent image data by the gain g are the same as those of theeighth embodiment, further explanation thereof has been omitted.According to the thirteenth embodiment: the narrow band fluorescentimage data NS′ and the wide band fluorescence image data WS′, which havebeen multiplied by the gain rg formed based on the reflectance imagedata RS, are inputted to the hue image data forming means 420. The hueimage data forming means 420 outputs the wide band fluorescent imagedata WS′ and the narrow band fluorescent image data NS′ to respectivelydifferent color planes (e.g., G and R), and forms, based on the additivecolor mixture method, a color added and mixed image data representing acolor added and mixed image ; then, by computing, based on this coloradded and mixed image data, the hue value of the color added and mixedimage represented by said color added and mixed image data and occurringin the Munsell color system, the hue image data forming means 420 formsa hue data value H.

On the other hand, the wide band fluorescent image data WS′, which hasbeen multiplied by the gain rg, is inputted to the luminosity image dataforming means 422; then, the luminosity image data forming means forms,based on the range of the pixel values of the wide band fluorescentimage represented by the wide band fluorescent image data WS′ and thelook-up table, a luminosity image data V determining a luminosity V(Value) occurring in the Munsell color system.

The hue image data H and the luminosity image data V are inputted to theimage composing means 424, and the image composing means 424 forms acomposite image data CS′. In this case, because a saturation is requiredin addition to the hue and luminosity, when the composite image CS′ isto be composed, the largest value of each hue and each luminosity is setas a saturation value S occurring in the Munsell color system, and thecomposite image data CS′ is formed by performing an RGB conversionprocess. In this manner, data relating to the tissue state of the targetsubject 50 as well as data relating to the form of the target subject 50can be displayed concurrently in a single image, the same as in thefifth embodiment.

Next, an endoscope implementing the fluorescence image obtainingapparatus according to the fourteenth embodiment of the presentinvention will be explained. According to the endoscope implementing thefluorescence image obtaining apparatus according to the fourteenthembodiment: the narrow band fluorescent image data NS′ and the wide bandfluorescent image data WS′, which have been multiplied by the gain rgformed based on the reflectance image data RS, as in the thirteenthembodiment, are subjected to a dynamic range expansion process, based onthe statistical quantity computed by the statistical quantity computingmeans 803. Therefore, as shown in FIG. 23, the image computing unit 400of the endoscope according to the fourteenth embodiment is provided witha dynamic range expanding means 826 for subjecting the wide bandfluorescent image data WS′, which has been multiplied by said gain rg,to a dynamic range expansion process. Note that because the dynamicrange expanding means 826 performs the same process as that performed bythe dynamic range expanding means 414 of the fourth embodiment, adetailed explanation thereof has been omitted.

In this manner, by providing the dynamic range expanding means 826,because the distribution of the luminosity image data V can be made tospan substantially the entire area of the display gradation curve of thecomposite image monitor 602, the contrast of the composite image formedthereof can be made higher. Accordingly, the change in the tissue stateof the target subject 50 can be represented more accurately in thecomposite image, whereby the distinguishability of the tissue state ofthe target subject 50 can be further improved.

Note that according to the fourteenth embodiment, the dynamic expansionprocess can be preset so as to be performed for each image, or can beperformed only when so desired by the operator of the endoscope, by useof a foot switch 210 or a hand operated switch 212, in the same manneras occurred in the fourth embodiment.

Further, according to the above-described thirteenth and fourteenthembodiments, although hue image data H and luminosity image data V havebeen formed in addition to the processes performed in the eighthembodiment, it is also possible that a hue image data H and luminosityimage data V be formed and combined to obtain a composite image data CS′in addition to the processes performed in the ninth through twelfthembodiments described above. In this case, according to the ninthembodiment, the hue image data H can be formed utilizing the reversenarrow band fluorescence image NS″; according to the tenth embodiment,the hue image data H can be formed utilizing the constant-multipliedreverse narrow band fluorescence image NS″. Further, according to theeleventh embodiment, the hue image data H can be formed utilizing thedifference data α Ssub, which has been multiplied by the constant α; andaccording to the twelfth embodiment, the hue image data H can be formedutilizing the wide band fluorescence image DWS′ and the narrow bandfluorescence image DNS′, which have been subjected to a dynamic rangeexpansion process.

Still further, according to the above-described thirteenth andfourteenth embodiments, although the luminosity image data V has beenformed, based on the wide band fluorescent image data WS′, which hasbeen multiplied by the gain rg, by the luminosity image data formingmeans 422, the luminosity image data V may also be formed based on thenarrow band fluorescent image data NS′, which has been multiplied by thegain rg.

In addition, according to the above-described thirteenth and fourteenthembodiments, the luminosity image data V has been formed, based on thewide band fluorescent image data WS′, which has been multiplied by thegain rg, by the luminosity image data forming means 422; however,according to the fifteenth embodiment shown in FIG. 24, the reflectanceimage data RS′ may also be multiplied by the gain rg, by the gainmultiplying means 405, to obtain a reflectance image data RS′, which hasbeen multiplied by the gain rg, and the luminosity image data V may alsobe formed based on this reflectance image data RS′, which has beenmultiplied by the gain rg.

Additionally, according to the above-described thirteenth and fourteenthembodiments, the luminosity image data V has been formed, based on thewide band fluorescent image data WS′, which has been multiplied by thegain rg, by the luminosity image data forming means 422; however,according to the sixteenth embodiment shown in FIG. 25, the luminosityimage data V may also be formed based on the wide band fluorescent imagedata WS, which has not yet been multiplied by the gain rg. Note thatneedless to say, the luminosity image data V can also be formed based onthe narrow band fluorescent image data NS or the reflectance image dataRS, which has not yet been multiplied by the gain rg. In this case, itis preferable that it be possible to switch the image data, based uponwhich the luminosity image data is to be formed, between that which hasnot yet been multiplied by the gain rg and that which has beenmultiplied by the gain rg.

Note that for cases in which the luminosity image data V has beenformed, based on the wide band fluorescent image data WS′, which hasbeen multiplied by the gain rg, because the gain changes by a largeamount if the distance between the target subject 50 and the distal endof the endoscope insertion portion 100 changes a large amount, thebrightness of the displayed composite image is also changed by a largeamount. Therefore, by forming the luminosity image data V based on thewide band fluorescent image data WS, which has not yet been multipliedby the gain rg, a large change in the brightness of the composite imagecan be prevented.

Note that according to the thirteenth through the sixteenth embodiments,although the hue image H (a uniform saturation) has been computed, theseembodiments are not limited thereto: an image corresponding to the theX,Y components of an XYZ color space; the ab components of a Lab colorspace; the uv components of a Luv color space; the a*b* components of auniform La*b* color space; the u*v* components of a uniform Lu*v* colorspace; etc., can also be computed.

Further, according to the first through the sixteenth embodimentsdescribed above, the statistical quantity computed by the statisticalquantity computing means 403, 803 can be computed based on fluorescentimage or the reflectance image obtained in the frame preceding the framein real time frame, instead of a single frame in real time frame of thefluorescent image or the reflectance image.

Still further, according to the first through the sixteenth embodiments,a standard image obtaining element 107 has been disposed in the distalend of the endoscope insertion portion 100; however, by utilizing animage fiber, the standard image obtaining element 107 can be disposedwithin the interior of the image data processing portion of theendoscope. Further, the standard image fiber, the fluorescent imagefiber and the image obtaining element can be provided in the form of acommon unit. In this case, the optical transmitting filter can beprovided with a filter for obtaining standard images. Still further, byproviding the image obtaining element with an on-chip mosaic filter thathas a functionality equivalent to that of the filter for obtainingstandard images with which the optical transmitting filter has beenprovided, the standard image obtaining element and the fluorescent imageobtaining element can be provided in the distal end portion of theendoscope insertion portion.

In addition, according to the composite image display method, a standardimage display monitor 601 and a composite image display monitor 602 havebeen provided separately; however, both said types of images can bedisplayed on a single monitor. In this case, the switching between thedisplay of the standard image and the composite image can beautomatically controlled in a temporal series manner by the controlcomputer, by use of an appropriate switching means to be operated by theoperator, or by a desired switching configuration. Further, the standardimage and the composite image may be superposed and displayed.

Additionally, the image fiber 103 can be provided as a composite glassfiber instead of a quartz glass fiber. In this case, because a compositeglass fiber emits fluorescent light when an excitation light enterstherein, an excitation light cutoff filter 302 must be provided betweenthe focusing lens 106 and the fluorescent light entry end of the imagefiber 103. By using a composite glass fiber instead of a quartz glassfiber, the cost can be reduced.

Note that according to the first through the sixteenth embodiments, thecomputational process of the image computing unit 400 are not limited tobeing performed on each pixel unit; the processes can be performed onthe pixel units corresponding to the binning process of the highsensitivity fluorescence image obtaining element, or on an arbitraryvertical by horizontal (n×m) block of pixels selected by the operator.

Further, any light source that emits light having a wavelength in the400–420 nm wavelength band can be selected as the excitation lightsource.

Still further, according to the first through the sixteenth embodiments,the excitation light source and the white light source have beenprovided separately; however, by employing an appropriate opticalfilter, a common light source can be employed.

1. An endoscopic fluorescence imaging apparatus comprising: afluorescence image obtaining means for irradiating a target subject withan excitation light and obtaining two fluorescence image data, eachformed of fluorescent light of a mutually different wavelength band witha filter having at least two individual bandpass filters filtering themutually different wavelength band, based on the fluorescent lightintensity emitted from the target subject upon the irradiation thereofby the excitation light, a gain computing means for computing, based onstatistical quantity of either one of said two fluorescence image data,a gain that said two fluorescence image data are to be multiplied by, amultiplying means for multiplying said two fluorescence image data bysaid gain and obtaining two multiplied fluorescence image data, an imageforming means for forming, based on said two multiplied fluorescenceimage data, a pseudo color image data representing a pseudo color imagereflecting the tissue state of the target subject, and an image displaymeans for displaying said pseudo color image.
 2. A fluorescence imagedisplay apparatus as defined in claim 1, wherein said image formingmeans is a means for forming the pseudo color image, based on anadditive color mixture method, from both of the multiplied fluorescenceimage data.
 3. A fluorescence image display apparatus as defined inclaim 1, wherein the image forming means comprises: a color imageforming means for forming a color added and mixed image data, based onan additive color mixture method, from both of the multipliedfluorescence image data, and a color image data, based on said coloradded and mixed image data, representing the chromatic components of thecolor added and mixed image represented by said color added and mixedimage data, a luminosity image forming means for forming a luminosityimage data representing a luminosity image by assigning a luminositydisplay gradation to the pixel values of the multiplied fluorescenceimage represented by either of the two multiplied fluorescence imagedata, and a composite image forming means for combining the color imagedata and the luminosity image data to form a pseudo color image data. 4.A fluorescence image display apparatus as defined in claim 1, furthercomprising a dynamic range expanding means for expanding, based on thestatistical quantity, the dynamic range of both of the multipliedfluorescence image data so that the dynamic range of each said imagedata spans substantially the entirety dynamic range of the displaymeans.
 5. A fluorescence image obtaining apparatus as defined in any ofthe claims 1, 2, 3, or 4, wherein a portion or the entirety of theilluminating means, the image obtaining means, and the readout means isprovided in the form of an endoscope provided with an insertion portionto be inserted into a body cavity of a patient.
 6. An endoscopicfluorescence imaging apparatus comprising: a fluorescence imageobtaining means for irradiating a target subject with an excitationlight and obtaining two fluorescence image data, each formed offluorescent light of a mutually different wavelength band with a filterhaving at least two individual bandpass filters filtering the mutuallydifferent wavelength band, based on the fluorescent light intensityemitted from the target subject upon the irradiation thereof by theexcitation light, a reflectance image obtaining means for irradiating atarget subject with a reference light and obtaining a reflectance imagedata, based on the intensity of the reference light reflected from thetarget subject upon the irradiation thereof by the reference light, again computing means for computing, based on the statistical quantity ofsaid reflectance image data, a gain that said two fluorescence imagedata are to be multiplied by, a multiplying means for multiplying saidtwo fluorescence image data by said gain to obtain two multipliedfluorescence image data, an image forming means for forming, based onsaid two multiplied fluorescence image data, a pseudo color image datarepresenting a pseudo color image reflecting the tissue state of thetarget subject, and an image display means for displaying said pseudocolor image.
 7. A fluorescence image display apparatus as defined inclaim 6, wherein said image forming means can also be a means forforming the pseudo color image, based on an additive color mixturemethod, from both of the multiplied fluorescence image data.
 8. Afluorescence image display apparatus as defined in claim 6, wherein theimage forming means comprises: a color image forming means for forming acolor added and mixed image data, based on an additive color mixturemethod, from both of the multiplied fluorescence image data, and a colorimage data, based on said color added and mixed image data, representingthe chromatic components of the color added and mixed image representedby said color added and mixed image data, a luminosity image formingmeans for obtaining a multiplied reflectance image data by multiplyingthe reflectance image data by said gain, and forming a luminosity imagedata representing a luminosity image by assigning a luminosity displaygradation to the pixel values of the multiplied reflectance image or thepixel values of the multiplied fluorescence image represented by eitherof the two multiplied fluorescence image data, and a composite imageforming means for combining the color image data and the luminosityimage data to form a pseudo color image data.
 9. The fluorescence imagedisplay apparatus as defined in claim 8, wherein the pseudo color imagedata designates state and form of the target subject, wherein said statecomprises at least a diseased state and a normal state.
 10. Thefluorescence image display apparatus as defined in claim 6, wherein thestatistical quantity comprises calculating at least one of: an averagevalue of at least one pixel of said reflectance image data and astandard deviation of at least one pixel of said reflectance image data,and wherein the gain computed based on the calculated statisticalquantity is applied to the two fluorescence image data.
 11. Thefluorescence image display apparatus as defined in claim 6, wherein thestatistical quantity is calculated using said reflectance image data,and the gain is computed based on the calculated statistical quantityand wherein, both of the fluorescence image data is multiplied by thesame computed gain.
 12. An endoscopic fluorescence imaging apparatuscomprising: a fluorescence image obtaining means for irradiating atarget subject with an excitation light and obtaining two fluorescenceimage data, each formed of fluorescent light of a mutually differentwavelength band with a filter having at least two individual bandpassfilters filtering the mutually different wavelength band, based on thefluorescent light intensity emitted from the target subject upon theirradiation thereof by the excitation light, a reflectance imageobtaining means for irradiating a target subject with a reference lightand obtaining a reflectance image data, based on the intensity of thereference light reflected from the target subject upon the irradiationthereof by the reference light, a gain computing means for computing,based on the statistical quantity of said reflectance image data, a gainthat said two fluorescence image data are to be multiplied by, amultiplying means for multiplying said two fluorescence image data andthe reflectance image data by said gain to obtain two multipliedfluorescence image data and a multiplied reflectance data, a differencecomputing means for computing the difference data between the multipliedreflectance image data and either of the two multiplied fluorescenceimage data, an image forming means for forming, based on said differencedata and the multiplied fluorescence image data that was not used in thecomputation of said difference data, a pseudo color image datarepresenting a pseudo color image reflecting the tissue state of thetarget subject, and an image display means for displaying said pseudocolor image.
 13. A fluorescence image display apparatus as defined inclaim 9, wherein said image forming means can also be a means forforming the pseudo color image, based on an additive color mixturemethod, from both of the multiplied fluorescence image data.
 14. Afluorescence image display apparatus as defined in claim 12, wherein theimage forming means comprises: a color image forming means for forming acolor added and mixed image data, based on an additive color mixturemethod, from the difference data and the multiplied fluorescence imagedata, and a color image data, based on said color added and mixed imagedata, representing the chromatic components of the color added and mixedimage represented by said color added and mixed image data, a luminosityimage forming means for assigning a luminosity display gradation to thepixel values of the multiplied reflectance image represented by themultiplied reflectance image data or the pixel values of the multipliedfluorescence image represented by either of the two multipliedfluorescence image data to form a luminosity image data representing aluminosity image, and a composite image forming means for combining thecolor image data and the luminosity image data to form a pseudo colorimage data.
 15. A fluorescence image display apparatus as defined in anyof the claim 6, 7, 8, 12, 13, or 14, further comprising a dynamic rangeexpanding means for expanding, based on the statistical quantity, thedynamic range of the reflectance image data and/or both of themultiplied fluorescence image data so that the dynamic range thereofspans substantially the entirety of the dynamic range of the displaymeans.
 16. A fluorescence image obtaining apparatus as defined in any ofthe claims 6, 7, 8, 12, 13, or 14, wherein a portion or the entirety ofthe illuminating means, the image obtaining means, and the readout meansis provided in the form of an endoscope provided with an insertionportion to be inserted into a body cavity of a patient.
 17. Afluorescence image obtaining apparatus as defined in claim 15, wherein aportion or the entirety of the illuminating means, the image obtainingmeans, and the readout means is provided in the form of an endoscopeprovided with an insertion portion to be inserted into a body cavity ofa patient.
 18. A fluorescence image display apparatus as defined in anyof the claims 6, 7, 8, 12, 13, or 14, wherein said image forming meansis a means for obtaining a reverse fluorescence image data by invertingthe light intensity of either of the multiplied fluorescence image data,and forming a pseudo color image based on this reverse fluorescenceimage data and the other multiplied fluorescence image data of the twomultiplied fluorescence image data.
 19. A fluorescence image displayapparatus as defined in claim 15, wherein said image forming means is ameans for obtaining a reverse fluorescence image data by inverting thelight intensity of either of the multiplied fluorescence image data, andforming a pseudo color image based on this reverse fluorescence imagedata and the other multiplied fluorescence image data of the twomultiplied fluorescence image data.
 20. A fluorescence image displayapparatus as defined in claim 16, wherein said image forming means is ameans for obtaining a reverse fluorescence image data by inverting thelight intensity of either of the multiplied fluorescence image data, andforming a pseudo color image based on this reverse fluorescence imagedata and the other multiplied fluorescence image data of the twomultiplied fluorescence image data.
 21. The fluorescence image displayapparatus as defined in claim 1, 6, or 12, wherein the statisticalquantity comprises calculating at least one of: an average value of atleast one pixel of one of said image data and a standard deviation of atleast one pixel of one of said image data.
 22. The fluorescence imagedisplay apparatus as defined in claim 1, 6, or 12, wherein the pseudocolor image data designates state of the target subject, wherein saidstate comprises at least a diseased state and a normal state.
 23. Thefluorescence image display apparatus as defined in claim 1, 6, or 12,wherein said one of the two fluorescence image data is a wide band imagedata and the other is a narrow band image data.
 24. The fluorescenceimage display apparatus as defined in claim 1, 6, or 12, wherein the twofluorescence image data are multiplied by the same gain, the gain isdetermined based on the statistical quantity calculated using one of thetwo fluorescence image data.
 25. The fluorescence image displayapparatus as defined in claims 1, 6, or 12, wherein each of the twofluorescence image data is multiplied by the gain, and wherein the gainis determined based on the statistical quantity calculated using one ofthe two fluorescence image data.